Was doing a compression test today and found cranking speed varied a bit with glow plugs out. Sometimes cranked slower (not real slow, but comparable to when normally starting it) and other times cranked pretty fast like I'd expect only making compression on one cylinder. Made it difficult to get accurate readings. Under 1 yr old group 31s with new 2/0 grounds and between batteries and 3/0 to starter. Started is unknown age and been doused in coolant at least twice from block heater issues. Is it time for a starter?