John,
It is pretty easy to see if the cylinder is OK or not, as far as the piston, Piston rings and valves are OK. Run a compression check! (Pull the center distributor wire out of the coil, ground it, so the engine won't start)

If you have low compression, then listen for hissing in the exhaust and fuel air intake areas. If there is no hissing there on a compression check then take the oil filler cap off and see if it hisses there. if it does then you have blow by the rings.

Before you do any of this, just pull the coil wire and crank the engine, listen for a pattern of sounds from the engine that sounds like this: chug, chug, chug, chug, and a faster chug. We call this an ear compression check. If one of the pistons turns much faster during the ear test it is telling you that there is a weak cylinder.

If that's the case then you will have to get into the mechanical causes for the low compression and you might want to move on to another car.

On the other hand if it tests ok on that cylinder as compared with others, then you certainly could charge on to fuel and electrical problems and sort it out or pass on the whole deal!
Regards

Woody

91 740T soon for sale

1989 S70 T5, just brought home