Yep Wally is right (again). Not a mechanic myself, but have rebuilt lots of motors, and brought quite a few classics back to life.
You only have to think about it for a few seconds... how does the oil get above the pistons? Only two routes... past the rings or past the valve guide seals. The end gaps in the rings of modern engines are pretty tight if the engine is in good nick, so any seepage is going to be minimal. If you are getting a lot of seepage past the rings or valve guide seals, your motor is basically poked!
Petrol does indeed go "off" more quickly these days, although stuff that won't run my somewhat fussy bike, seems to work fine in the old Briggs and Stratton mower...
