93 gmc problems

[94sierra16]

I have a 93 gmc sierra with 235k miles on motor and around 15k on tranny. Ive been having some problems with it and it all started after i changed the oil. Now its getting oil on the first cylinder spark plug.And now I'm running 20 weight 50 oil. And it still does it but dont burn it as much. And its been missing and i just changed the spark plug and its still acting like its missing and idleing rough. Can someone help me out?

[jham0077]

I'd check the compression on that cylinder. Sounds like you either have valve seal/seat issues or a broke ring maybe.