What causes a rear main seal leak?

[bloopbloob]

I was just under my car today, and noticed a bit of oil. it was getting dark, but i'm thinking its the rear main. I've had the rear main seal replaced once before, then once again 2 days later because it blew out (bad install, which was coverered by warranty). now i think its leaking again, but its a slow leak compared to the 2 geysers i had to deal with before.... so why is this happening?

 

[88mouse]

There just bad about eating up rear main seals. A guy around here put a vac pump on the crank case. Never had a probablem with rear mains after that.

 

[HISSIN50]

Yep, as far as causes that are easy to check/fix, ensuring the crankcase ventillation is adequate (like 88Mouse said) is important. If the pressure bottlenecks, it goes for the path of next-least resistance, which is often the RMS.

Good luck.