on an m50 its always best, though, to suspect either the pump or air in the system....
seems like it is always one or the other....

a while back we changed a bunch of cooling hoses, radiator, etc. on my wife's 525 and couldn't get rid of a persistent leak right at the lower radiator hose below the expansion tank. finally turned out to be a tiny hole in the hose itself; sometimes even new parts aren't good!

and, yes, i do get calls quite often - its either for a car or a computer....both sometimes equally frustrating!