akscubaduck1:
I found that it just traps salt water inside your first stage.
The Mk 10 uses small holes in the ambient chamber about 1/16" in diameter. The idea was for them to be large enough to let water in to act on the environmental silicone inside the ambient chamber but to be small enough to make it hard for the silicone to ooze out (it still did in hot weather).
Later Mk 10's and Mk 10+ regulators had a groove cut in the first stage just in front of the yoke to hold a hard rubber boot to seal off the larger (about 3/16" diameter) holes into the ambient chamber. On these SPEC (Silicone Protected Environmental Chamber) booted regs, you can turn the boot to align the holes in the boot withthe holes in the first stage when diving it without silicone in the ambient chamber or rotate the boot to cover the holes to retain the silicone when it was silicone filled.
The small holes in the early Mk 10 make it hard to rinse as they limit water transfer. It's not a bad idea to get a dust cap that fully seals the first stage inlet (tested by sucking hard through the second stage with it installed and gettin NO air at all) and then soak the first stage after each dive day or dive trip in hot tap water to remove salt.
This older style also has less heat transfer due to less water flow through the ambient chamber and they are more likely to freeze up in very cold water if the ambient chamber is not silicone filled. Although I have never had one freeze up on anything short of an ice dive. If you consider 45 to 60 degree water to be "cold" you will never have a problem.
The later style Mk 10 is both easier to rinse and more cold water freindly without silicone in the ambient chamber. Scubapro moved away from silicone filled ambient chambers entirely about a decade ago when they switched to Christolube for nitrox compatibility. Consequently, SPEC boots and environmental silicone are no longer available from Scubapro and silicone will not be installed during an annual service.
Corrosion in the ambient chamber is probably the biggest killer of older Mk 10's as the ambient chamber is in the body of the first stage rather than in an easy and inexpensive to replace swivel cap as is the case with the Mk 5, Mk 15, Mk 20 and Mk 25.
The Mk 9, Mk 10 and Mk 10+ were the only first stages SP ever designed that had the ambient chamber in the body and it was with good reason they went back to the basic Mk 5 design in their later first stage designs. This is the only inherent weakness in the Mk 10 design but it is not really an issue on the later Mk 10's and Mk 10+'s and it is not a serious issue on an earlier Mk 10's as long as they are properly rinsed.
To put it in perspective, I see a large number of these first stages in for service every year (more than any other single model) and perhaps only one per year has to be retired due to corrosion or wear in the first stage body and the cost of repair versus replacement. This is an excellent statement about Mk 10 durability when you consider that these first stages are all 12 to 25 years old.
