familyman
I ran all my 240s on unleaded. That includes a 1976 for about 7 years, and a 1978 for 9 years. No ill effects. No lead additive. I think the confusion rises from the 'compatibility charts/books' Australia printed.
Sweden/Europe had unleaded-designed engines yonks before us. While leaded fuel works in unleaded-designed engines, the opposite isn't necessarily true. But in the 70s many petrol stations (that I saw anyway) had only 1 or 2 diesel pumps, and the rest were super (leaded), except for 1 or 2 standard (unleaded) pump/s. And often one of those, or that single standard pump, was off in a corner away from the other pumps. I clearly remember on Saturdays dads would fill their cars with leaded ready for work on Monday, then walk over to the standard pump where there was a constant stream of other dads or the occasional mum filling their 5L metal Victa 2-stroke tins to mow their lawn.
Then pump numbers evened out to 'super' and 'unleaded' (the word 'standard' disappeared). Then leaded went.
Anyway, we had plenty of leaded-designed cars and the number of leaded pumps reflected that. So for unleaded/European car owners, the petrol companies and/or government - whoever it was... probably required a lead canister/pollution gear fitted, then told Volvo owners leaded fuel was ok in their engines.
When leaded was later removed from sale, the NEXT lot of 'compatibility' books/info changed 'has the ABILITY to use leaded fuel' to: 'can ONLY use leaded fuel' (and so must need a lead additive). Even though the previous year probably had the same engine fitted at the factory.
Over the years I've seen several late 240s on ebay (which happily ran unleaded fuel in Europe) with: "Lead additive system fitted by mechanic" in the auction description. While they were spending $$ continually topping up their lead additive, I drove my 2x 1970s models on unleaded for ~16 years. So Volvo fitted pollution gear so owners could 'legally' use leaded fuel; then when leaded fuel was banned some mechanics fitted a lead additive system because they saw the engine had lead pollution gear/canister fitted. When they could have just ran unleaded fuel and/or ripped the pollution gear out, because with no leaded fuel available it was no longer needed, and wasn't on the same engines in Europe anyway.
ramrod
Those "mechanics" had no idea what they were doing. They fail to understand that all engines fitted with aluminium cylinder heads already have hardened valve seat inserts.
This is a moot point anyway, since leaded fuel hasn't been available for over 10 years, not sure why we are even discussing it