Oil leaks on 104s are more often than not the valve cover gasket and the front timing cover seal.

Neither is expensive, just somewhat time consuming and intimidating for the novice.

If the oil is free of coolant and coolant free of oil it is relatively safe to assume that the head gasket is -currently- in decent shape.

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David Hendy
'97 Renntech E60RS
'97 GMC 2500 Sub' Diesel
'95 E300D
'88 300TE
'88 250TD
'84 L/Rover 109