I once tried to sell my Game-Master, received a couple of decent offers, then had second thoughts, and so it remains in my collection.
Below I am showing the listing of this Game-Master (with the price deleted), as it shows the timepiece in near mint / NOS condition. (If it doesn't display properly in this frame, you can Click Here to see the page in a new browser.)
The parts for this stopwatch should be readily available; inside the case, it is a fairly common 60-minute stopwatch. The crown on the left locks the bezel in place, and is probably a unique piece for the Game-Master.
I would certainly understand if you decide to keep this one. They are really nice pieces, and in my view, they seem to be undervalued at the moment.
Jeff