There is no real reason to replace a Mk 5 first stage unless the body is worn out and it is experienceing problems with HP O-ring pinch. The Mk 5 uses a very nice flow through piston with a large diameter head that provides for very stable intermedate pressure - better than the Mk 10 with it's smaller piston head. Service kits are still available for the Mk V and they incorporate the latest changes in seat technology. If your mark V has the newer 4 or 5 port swivel cap, there is no reason not to use it if it is in good shape internally. The yoke on the early Mk 5's were designed for 2250 psi tanks and they will eventually fail if used on a 3000 psi tank. Even the slightly later yokes marked 3000 psi should be replaced if they are not the heavy yoke that uses the current large sized yoke screw. Again this is not an issue as the yoke is available from SP.
If the body is in fact worn to the point of needing replaced, or if the first stage needs a lot of updating and you decide not to pursue it, let me know, I'd be interested in buying it from you as is.
It is hard to say exactly what you have for a second stage. It is either an Adjustable or a Balanced Adjustable. An Adjustable can be upgraded to the 4th configuration of the Balanced Adjustable that uses the latest S-wing poppet and the balance chamber and spring used in the later model G250's. The dealer cost of the parts to do this is under $20 and all but the spring (a $1.00 item) come in the annual service kit for the G250 anyway, which is also used for the Balanced Adjustable.
Upgrading one in this way gives it cracking effort and brething performance comparable to the S600 with a similar overall size that is much smaller than a G250 but that takes advantage of the full sized diaphragm use din the G250. You don't have an adjustbale Viva knob, but that is no great loss. An added advantage is that the metal case has excellent heat tranfer traits which make it ideal for cold water and the metal case tends to cause condensation of your exhaled moisture and a eliminates dry mouth. Dry mouth can be a problem in the newer graphite cased regs, particularly those with plastic air barrels. A fully modernized Balanced Adjustable is, in my opinion, the best conventional style reg available new or used.
Alternatively if it is an Adjustable and you do not want to upgrade, you can replace the poppet assembly with a newer and lighter version with a replaceable seat. And again the service kit is still made. But personally, given the very minor differnece in parts cost, it makes a lot more sense to go with the upgrade.
Occassionally I encounter a lever that needs to be changed as some of the early Adjustables had levers that will not work with the new poppets due to slight differences in the shape of the tabs. But again this is not a horribly expensive part to replace
The power inflators on the original stabilizing jacket, as well as the double blue and double black jackets that followed used a different quick disconnect. At that time, every manufactuerer used their own proprietary design, which made matching rental regs to rental BC's a pain. The inflators are failry simple and easy to repair, but the hoses are very rare, so unless you have the hose, you have a paper weight. It makes more sense anyway to upgrade to a new balanced inflator. They work better and will use a standard LP quick disconnect.
The stab jacket was very durable, particularly the double blue and double black versions with rubber on each side of the nylon. The double blue jackets were made by calendaring the blue rubber over the orange fabric for the stab jacket. Overtime the orange dye bled through the outer layer of rubber and turned them a moldy green color. Scubapro replaced them under warranty with double black jackets though, so double blue hackets are also very scarce.
The down fall of most of the originial Scubapro stab jackets was the seams. They tend to develop leaks with age especially in the front where the seam forms a crease. The seam tapes was just not as durable as the fabric used in the jacket. Often you can use neoprene cement applied though a long plastic tube through the inflator and dump holes to neatly seal these leaky seams from the inside. It takes some care and patience but can get you a few more years out of a vintage stab jacket if it is otherwise in good shape.
And I agree with you completely about the current attitude toward equipment. The modern technical philosophy has a lot going for it, but it is a logical fallacy to say that because it is ideal for a techical dive, that it will be optimum for all types of diving. There are a lot of recreational divers who really gain nothing from a technical configuration but are made to feel inadequate with out it.
There is no harm in techncally oriented DIR types stating opinions, but it often goes beyond that with some of them sanctimoniously saying that it is not safe to do it any other way. And to make it worse they often do it based on dogma learned in a classroom rather than based on real world experience and caseful consideration for the needs of the individual diver and the requirements of the dive itself.
Similarly, there has been no substantial improvement in regulator design in the last 2 decades. Case design has changed with the use of composites and phenolic resins but this was motivated more by efforts to cut production costs than to gain any radical improvement in breathing performance. Very few if any new regs breathe better than a top of the line 20 yr old design like the MK 10 Balanced Adjustable or MK 10 D400. Many, if not most new regs are lucky if they breathe as well, particularly given the design compromises required for CE approval which as a whole tend to require the reg to be detuned to meet unrealistic and unnecasarily harsh freeflow standards.
But then that's just an opinion from someone who puts all the technical stuff away now and dives with my 44 yr old DA Aquamaster and 43 year old Mistral double hose regs and a Scubapro horse collar BC with an oral inflator.
