Hi,
It's a 1992 I've owned since new. Small puddle forming underneath and looked to be seeping from the base of the reservoir where it attaches to the radiator housing. Most (here and elsewhere) suggested replacing the entire radiator but I could not resist the possibility that only $8 of o-rings might be all that was required vs. a $400+ radiator.
I drained the radiator, but not the block, removed one radiator clamp (amazingly without it breaking), removed the upper retaining plate and then gently pried the tank out. Once out, I cleaned the o-ring areas etc, lubed the new ones with coolant, installed them and then gently tapped the tank back in place (using wood block to buffer the mallet).
So far I've recorded about 500 miles on it without a drop of coolant showing. Maybe I was lucky for once, but had to at least give it a try. Too, I have the luxury (if you want to call it that) of another vehicle to drive were it not to have worked.
Also, I read a lot indicating "USE ONLY BMW COOLANT!". Per two different parts guys at the BMW dealer, the only real requirement is for the coolant be void of nitrates and be non-phosphorous. Today the guy said he knew Zerex made one (looks like it's their G-50). I use Prestone Extended Life which has no nitrates or phosphorous.
Happy driving, Nate