OK, you want to learn from others *mistakes*...........
I have in Malaysia my own and two brothers cars as follows, all running on unleaded WITHOUT any additives or valve/seat replacement.
1. 1976 W115 200
2. 1979 W116 450SEL
3. 1972 Alfa GTV
4. 1975 BMW 3.0Si
5. 1979 BMW 525
6. 1980 BMW 628CSi
7. 1982 Volvo 240 B21A
In the US, I ran a 1966 VW Karmann-Ghia (original heads and everything) on unleaded regular gasoline without any problems whatsoever. I always check engine compression on all cars that I own once a year and Ghia had 120psi when I got it in 1998 and left my ownership in 2001 with 115-120psi.
The valve seat recession issue only affects engines with cast iron heads where the seat is cut directly into the iron head, without an insert.
DB gasoline engines have:
1. sodium filled exhaust valve stems
2. stellited seats
The *official* line from DB was that all engines manufactured before 1985 (introduction of W124) cannot run unleaded without retarding timing and halving valve adjustment intervals. If the engines are being ruined by unleaded, how does DB explain all the W114/115/116/123s still in regular use in Germany with the Wurm catalyser?
If you are still not convinced, ask an experienced parts man to cross check the part nos. for the valve seats for the US market M110 and the ROW(rest of the world) M110. I would not be the least bit surprised if it is the same. I do know that ALL Alfa Romeo 4 cylinder twin cam engines used the same part no exhaustvalves and seats for all markets from 1970 onwards.
Have a good week.