Quote Originally Posted by Anton CH.
I had the same problem, one of the o-rings had an extremly slow leak (I think it was the lower one) even after o-ring replacement. I just gave up on it and bought another radiator. I believe the m50 has a very poorly disigned expansion tank. With age, things do not align as well as they should. I thought about trying and experimenting with larger o-ring/sealent but the thought of removing the radiator outweighed any savings for me.
I can see into the top of the expansion tank and see a slight weeping of fluid from the top o-ring.
Which, in turn, runs down the black plastic portion, into the larger o-ring's well, fills it then dribbles down onto the lower rad. hose onto the core support.
I've replaced both o-rings already. I'm wondering if the upper o-ring's hole is messed up somehow? I didn't SEE any scratches/damage but it doesn't take but a teeny scratch to produce a leak.

A new radiator just isn't in the funds right now.
I spent up a blue streak on the car in the past month. Ouch.

Thanks,
Bill