Mate be careful, apart from the engine I've heard its a **** box. Go to a 7 series forum and see what they reckon.
The 750 has no transmission problems.
Only the 740V8 and the European 730V8 with the 5HP30 trans, same like the E34 540.

You do not have to go to a 7 series forum, because I am answering also there as the authority for E32 750

Basically it is very easy. Fuel prices are high = these cars are sitting at the dealers and no one wants to buy them except some guys like me.
My calculation however is different. I do not drive a lot, less than 5 K miles per year, I can get a luxury car with a 12-cylinder for a bargain price, I repair them as I have the skills, the diagnostic tools, the special tools, and spare parts cars, and it is my hobby.
That makes it very cheap in maintenance for me.

BUT in case you have to bring the car to the dealer for every small problem, it will cost you a fortune to maintain it. It was a luxury top of the line car, the parts prices are still top of the line, and you do not find many skilled technicians for this car, as they maybe have to work on a 750 once a year or have never done before so, depending on where you live.