My current and preferred technical diving regs are a pair of Mk 17's with 1990's vintage G250 second stages. So my personal advice would be to go with a new Mk 17 first stage.
On the other hand, there are a lot of used Mk 10s floating around and buying another one (or a Mk 15 or Mk 20) in very good condition is not all that hard.
I don't neccesarily disagree with the conspiracy theory that your Mk 10 is not all that hard to fix but the shop won't because they want to sell you a new reg. Some SP sales reps and the whole sales structure itself tends to pressure dealers into selling new regs rather than servicing old ones. If you are the orginal owner and it is under warranty, see what they will do about warranty replacement of the Mk 10.
On the other hand, there are a lot of used Mk 10s floating around and buying another one (or a Mk 15 or Mk 20) in very good condition is not all that hard.
I don't neccesarily disagree with the conspiracy theory that your Mk 10 is not all that hard to fix but the shop won't because they want to sell you a new reg. Some SP sales reps and the whole sales structure itself tends to pressure dealers into selling new regs rather than servicing old ones. If you are the orginal owner and it is under warranty, see what they will do about warranty replacement of the Mk 10.