I've read that you can gain a hp or 2 from going over to synthetic/fully synthetic oil. My question is, do I risk it on my 90 b12 with 140,000 miles on it? I had my engine flushed and cleaned with solvent a few thousand miles ago and it hasn't started to leak yet. I do have a small leak in the O ring behind the distributor I just have to get that fixed. Any opinions?