from what you just put id say you def have a problem with that cylinder mate!!!!!!!!
does it breath at all ???????? (could have done commpression rings on that cylinder my mates skyline just has did not use oil either just broke a lump off corner of piston it did not even knock just started noticin it was breathin heavy
or possibly slightly bent a valve
it sounded ok though when i last heard it ???? not as though it has a bent valve any way unless is very slight????