Not sure what that grease does but hopefully does not reduce the ground path the plugs need.

Compression test only reports max PSI and not if there are any leaks in intake or exhaust.

Leak down test your using an air compressor to inject high pressure into cylinder and then tool has 2 gauges to see what the incoming pressure was and you leave in for awhile and the other gauge then shows over that time if the pressure in the cylnder side is leaking down due to ring or head problems

Leakdown tool is cheap and then needing the air compressor