I'm not using high mileage oils at all....and that's a great question, since when is it not good for seals?
I did have HM PS fluid in it until i decided to run ARX (the maxlife PS fluid actually slowed the leak!)....before adding the ARX, actually a week prior, i flushed the system, then topped it off and added the 1oz of ARX. I visited the site, read the entire site, and printed half the site...
and BTW
well, o2 sensor didn't make it in...totally stripped, heated with torch, etc. bolt in there for now.
new fuel filter ...NO hesitation/surge anymore.
not sure which it was, the O2 or filter. the filter was new after the junkyard tank (with lots of varnish...) I'm thinking the Techron dissolved it all and put it in the filter, that gas was nasty coming out...
after looking on rockauto.com, the manifold with both gaskets and new hardware was $77....just the one gasket was $16...so, i figured I'd just pay for the manifold/hardware kit instead...that way, no tapping and I'll be sure the O2 sensor fit...expensive lesson considering I'm now driving around with the CEL on the whole time and she runs/idles like a champ.