Sorry to bother you guys again but please help

Six months ago, while driving my faithful 190e 2.6 with automatic transmission, the car wouldn't upshift and would only go 35-40 mph. The next day I tried to start the car and it wouldn't start, a lot of fluids leaked from under the car. Due to other problems that the car had--needed new heater core, no aircondition, oil leaks. I decided to leave the car alone and buy another one---1996 VW Passat GLX which has since been wrecked.

Six months later I would like to revive the 190e, my mechanic told me he could replace the transmission with a used transmission for $1400, now what I was wondering is how can I find out if the problem is something else, like a kickdown switch e.t.c and what other damage have I done to the car by letting it sit for six months. If the problem is the transmission, I will replace it but I don't want to replace it and find out the problem is something else, shouldn't the car have started despite the transmission going bad.

Any suggestions on where to start diagnosing the problem, my mech already has the idea in his head that it needs another transmission, but I could tell him to try something else before replacing the transmission.

Thanks for any advice you can give.