Oil type & OCI advice for Air-Cooled car engine

[FCD]

I might be wrong but I think at leaswt 90% oils in the market in EU are rated for both, gasoline and diesel. So whichever I'd choose would be 'HDEO' (I assume so...)

You are correct that most oils sold in Europe are rated for both Gasoline and Diesel such as A3 ( Gas ) and B4 ( Diesel ) however these are not HDEOs, these are light duty passenger car oils, the term HDEO refers to oils made for Heavy duty Diesel engines like the ones used in large truck engines.
I think a 15W40 HDEO like Shell Rimula R4X or Mobil Delvac MX would be good choices, these are true HDEOs but they are also approved for Gasoline engines, both are API SL and CI-4.

 

[SR5]

I think a 15W40 HDEO like Shell Rimula R4X or Mobil Delvac MX would be good choices, these are true HDEOs but they are also approved for Gasoline engines, both are API SL and CI-4.

That would be my choice too, a mixed fleet (petrol and diesel engines) HDEO 15W40 like Shell Rimula R4X or Mobil Delvac MX.

Both are old school 15W40 oils with API CI-4 / SL, and Euro ACEA E7.
Old tech oils by today's standards, but still much better than anything Comrade Leonid Brezhnev would have given it in 1978.

BTW does anybody ever run two extra hoses, to and from a conventional oil filter, mounted discretely in the engine bay? To add a bit of oil capacity and extra filtration?

If you are only doing around 1200 km per year in summer, I would just change the oil once per year, just before you put it away for the winter.

 

[hid3]

If you are only doing around 1200 km per year in summer, I would just change the oil once per year, just before you put it away for the winter.

Thanks. Would it be a big deal if I'd be changing the oil not annually but bi-yearly instead? Removing and cleaning centrifuge is a bit messy and there's a complex shaped gasket in between (which is supposed to be one time use but it's been re-sealed using RTV multiple times)

 

[SR5]

Thanks. Would it be a big deal if I'd be changing the oil not annually but bi-yearly instead? Removing and cleaning centrifuge is a bit messy and there's a complex shaped gasket in between (which is supposed to be one time use but it's been re-sealed using RTV multiple times)

Yes, I think you should be fine to go 2 years at that low mileage. I have done similar things myself on some of my old motorcycles.