Welcome - don't over think the issue too much. Any good quality 10w30 will do just fine [the straight 30 spec was made prior to 10w30 availability] The real issue is time and use between oil changes and winter lay up with new clean oil. There is an old Universal motors 50 hr running rule for oil change sequences but I am not sure the engineers were thinking about A4's being in service 40+yrs after production was halted in 1979 especially engines with out filters.. Modern day detergent oils hold combustion/wear particles in suspension which in theory can decrease the oil's lubricity over time. I live in Chicago with a relatively short season - May thru Oct. I recommend to all A4's in the harbor changing oil for the winter layup just prior to haul out AND mid season, probably something like 20 -30 hrs of total running time [lake is a few hundred yards from the docks]. This assure clean oil lubricating bearings etc and is cheap insurance. As a testament I have a 1966 A4 and has never needed rebuilding and still going strong. [Use to change the oil an additional time in the spring time at launch after winter layup but I convinced myself long ago that this unnecessary and wasteful].
Relative to the amount of oil you should check the dipstick and it roughly changes with installation angle of the engine. I have a Morgan 34, pretty level [0 to 5 degrees] I use 4 1/2qts. On a lady friends 27ft Oday with about 15degree slant we use 3qts.
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