I started my '92 on synthetic w/ 120k on it and at first it used more oil than normal but after a while it seems to have gotten used to it :hsdunno:
Previously w/ the dino in there it took 1/2 bottle of seal conditioner to stop the small amount of oil use.
I stopped using that to see if the consumption came back and it did, I then switched to the synthetic and added the seal conditioner again but it continued using oil at a faster than normal rate, even after adding the other 1/2 bottle of conditioner.
Finally, after about 2000 miles the oil use has slowed to almost nothing so I'll continue to use synthetic for the improved mileage, smoother idle, and extended service intervals.
I've heard that Mobil 1, maybe just some kinds(I've got Extended Performance in there now), will tend to result in more oil consumption but until I try Castrol Syntec on my next change I can't say for sure.