I have an old 1961 Fordson Super Major 4 cylinder, non-turbocharged diesel tractor that my grandfather bought in '61, and still serves us to this day. Through the 60's and 70's when my grandfather farmerd full time, it saw lots of work and was probably well taken care of. Since then, maintenance is a little slack. About three years ago I put Mobil 1 5W-30 in the crankcase, and recently sampled it for fun mostly. The oil was plenty dark, but looked okay, very few hours are put on the tractor anymore.

code:
Iron            34
Chromium 0
Lead 13
Copper 32
Tin 0
Aluminum 5
Nickel 0
Silver 0
Silicon 24
Boron 49
Sodium 48 CRITICAL
Magnesium 954
Calcium 922
Barium 0
Phosphorus 624
Zinc 782
Moly 3
Potassium 57 CRITICAL
Fuel <1
Visc@100 9.69
Water 0
Soot/Solids .01
Glycol POS CRITICAL
Nitration 15
Oxidation 18
TBN 9.09

So, obviously some sort of coolant leak. I replaced the head gasket 4 or 5 years ago, and while I did a good job, it wasn't a top notch job. Additives seem depleted, but TBN is holding strong. Bottom line, wear is not too bad in my opinion.