I don't know how but apparently I missed this whole thread. I admit I didn't read the thread word for word. There are a couple of things that are glaring, when your guy overhauled the carbs. they apparently didn't clean the fuel delivery system, ie replace the grey tempo hoses, replace the fuel control valve, etc.
This is like closing the barn door after the horses are out. Your carbs. are just going to get clogged again, causing your ski to bog.
I'm not sure what is causing the leak, the best way to find out is to either ride it with the seat off and look, or back the ski attached to the trailer in the water and see if you can tell where the leak is. Places to check are the carbon seal and look for any leaks in the exhaust pipe. An exhaust leak would also cause your ski to run badly because it's trying to run on carbon monoxide and less oxygen.
Despite a common conception Lexington is not next to Louisville, we're about 1-1/2 hours away, but I would imagine when you go to Nolin Lake you come through here. I'm not a professional mechanic, just a shade tree mechanic like most guys on this forum, but if you want to swing by sometime I will be glad to look at your ski, maybe even fix it. I also have a 96GTI, and it's been a great ski.
Lou