just bought a 400 commander and 3 classic 3 diesel welders all around 98's with somwhere in the range of 12000 to 14000 hrs on em from an iron company paid 3500 for all 4, one of the classics is puking oil out the head gasket and wont start but the other 3 seem to weld and run good even cranked up. so my question is what typically goes wrong with these around this age and what kind of life expectancy? did i get a good deal???? btw had an account along time ago and read the forum daily just cant seem to remember my info, thx in advance