Hi just brought my first RR P38. 4.6. 1997. 112000 miles.LPG but running on petrol at the moment. Afew bits a bobs need doing but main issue is a misfire. (left bank as you look at it 2nd pot from front). did a compression test and only got about 40 psi. Thinking a burnt valve? No over heating,drove it 150 miles home and all ok didnt even pressurise. Seems to run better at about 2000 revs + but that may just be me! The spark plug for that pot was very sooty. Do they stick? or do they burn??

turns out it was the head gasket

at that milage check the cam as well for wear