This mower is 15 yrs old,lots of hours on it.Oil started last year or so.It starts coming out after running 5 mins or so.Enough to make noticeable smoke from the hot muffler,and dripping on ground.Is it time for engine work?....Is there a blocked pcv valve somewhere?
...ummmm, mostly logic built from the info so I can only offer
"pcv valve" may have collapsed, you could get that lucky at those
amount of hours. However you are reporting a heavily pressurised
c'case which would have had a working valve choking the carby feed,
long before this. I'd bet on a broken ring, or two.
Good news is,,, at that age you likely have a reasonable case to rebuild
or simply hone and replace with OS rings.
KK