Seadoo stuff is not like other boat stuff, the tachs can be replaced fairly easily but the speedo has a completely different design from what I have seen, i think it's electromechanical. You can use PWC gauges but they won't light up. Hence the reason an old used sun baked tach for one of our boats is $80-100 online. FYI the 96 and down gauges are not the same and while they can be made to function, the back light will not work quite the same, and I don't know if 94-95 even had backlights.
Whatever you do don't try to take them apart thinking you can fix them. The case plastic is too brittle and will not make it. Some of my gauges actually were starting to crack around the rim where they touch the hood and were allowing a lot of water in. Nothing some marine goop can't fix.