You are right. I did the exploratory today, and found my fuel leak in two places. One at the pump (gonna need a new one) and the other at the plug on the rear cylinder.
The plug leak was only an ounce or two an hour leak, the pump was a steady flow which turned to an engine-soaking spray when under pressure (driving conditions).
As far as the valve-stem seals go, I knew I was going to need them sooner or later. My oil burn is getting progressively worse over the past two years. The usual is about a quart between oil changes and the change always yields a quart lighter than the re-fill (in other words, NORMAL). I guess that since I am now doubling the burn, it is time to break down and change those seals.
The good news is that my compression is good on all cylinders so I don't need to worry about rings yet.
I am going to buy the donor car anyway. I could use the motor, trans, and other parts in the future (some now). I may as well buy the whole car for $500 now, or spend that same money on ONE Part from another one later.
76 240D (W115) - 550K miles
78 300D (W123) - 200K+ miles