I remember driving an Eldo for a period around 1983. The 4100 sure wasn't like the 1970 V8-500 that first turned me on to FWD, but the overall package was a nicely-sized and appointed car for in-town errands. (And the 500 ran short of breath at 75+ . . unlike a Chrysler T'NT 440).
I would go with an oil on the lighter end of the scale (per manual) and change it yearly. A low-restriction oil filter, too. LUBE CONTROL was my choice for the older cars I recently had to let go of, and they were on a 6000-mile/1-year program with MOBIL ONE and BALDWIN B2-HPG.
Not to mention plenty of FUEL POWER.