Sounds like a good candidate for synthetics, then. Have the rings sealed well?
Do you know whether there's a significant difference in synthetics?
Yah, there can be, mostly in pour point and ash temperature. There shouldn't be
any problem mixing synthetics and regular oil. There's a summary of oil types
and characteristics that makes its way around the net from time to time - the
basic gist is that AMSoil and RedLine are probably the best, but also the most
expensive. Of the next tier, Mobil 1 is the best - it's what I use. I remember
looking at the Castrol synthetic, and there were a couple of things about it
that made me decide against.