I don't have too much tech data on the 103 engine, but I do have an oil system schematic for the 102 engine in my "Model Year 1984" D-B manual.
Indeed, the oil transfer passage to the head is at the right rear of the block, so an oil leak at the head/block interface in this area would make the head gasket suspect, but if the leak is minor it could be left alone until the cylinder seal goes or coolant begins to leak. Minor oil leaks are a nuisance, but don't have much potential for consequential damage.
I had a similar problem many years ago on my '72 Vega GT. Oil seepage began at the right front of the block/head interface where the oil transfer passage to the head resides, and since the car was still on warranty I had the dealer replace the head gasket, and the problem did not reoccur.
The shop in San Clemente, CA that replaced the valve guides in my Cosworth Vega head last year (the owner also has a CV and just finished a complete rebuild) primarily works on Merc and BMW heads and has a steady flow of business. He says the guides wear fairly quickly because they are relatively short.
If one were to pull the head to change the gasket, it would probably be a good idea to go ahead and have the head completely refreshed to include new valve guides, valves (if necessary due to stem wear or seat condition) and valve seals along with a reseat of the valves, pressure test, and head surface check. Even if a head measures flat most shops like to take a .005" cut to ensure that all the old gasket is removed and the head surface is dead level. That virtually guarantees a good seal as long as the head gasket design is okay.
With a fresh head and a good gasket, the engine should run at least another 100K miles without major attention.