trans leak

[we350z]

Something is leaking from underneath my 2000 X5 that I just got It looks red and somewhat oily so I am guessing it is transmission fluid. I have had the car for about 2 weeks now and have been driving it regularly, and did not notice it until I was pulling back into my garage after work today. The car has just over 65Kmi on it, but obviously is 8 years old now.

I bought this car from my dad for $17K, because he was having difficulty selling it. One guy almost bought the car for $20K, but backed out when he had the car checked out at an independent mechanic, the reason: the mechanic said the transmission had a very small leak and it would cost around $1000 to fix.

My dad didn't believe him, but I guess he was right. Anyway he said he would pay to get it fixed if it really needed repair. In reality I might have to pick up half of the bill, but what exactly should I expect for an estimate from an independent mechanic?

I know the car has been taken care of and serviced at the regularly reccomended intervervals by BMW dealerships and independent mechanics.

I am not sure what exactly will need to be replaced, my guess is some sort of seal (I have heard rear main seal - which I know goes around the flywheel). I have watched this be done on my '93 300X TT when I installed an aftermarket clutch/flywheel), we also replaced the transmission mount as well since it was sagging a little (i think this sometimes is the cause of such leaks).

Any I a novice mechanic I have installed fuel rails and fuel injectors in my 300Z which required me to do some light fabrication, I have done bolt on modifications, changed oil, etc...

Any advice appreciated.