M103's and M104s tend to leak from the upper timing cover some and from the head gaskets. Not a real serious issue. You want to stop the leak? Reseal the top end, otherwise drive it. Normally I do a valve job on the 103 around 150k and 104 headgaskets around 120k.
I've also seen 104's leak from the Cam advance soliniod and the center of the cam sensor. On somewhat rarer occasions, oil pan and rear seal on both engines.
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