The problem with this one is "your mileage may vary". BMW had a couple of attempts at making heads that were guaranteed to live with unleaded, they made some mis-steps.
In very broad terms, if your head was made 1985 on it probably has the last iteration valve seats and is OK.
If your head was made 1981 update (big valves) to 1984 it might be OK - use additive to be sure.
If your head was made 1979 to 1980 (pre-update small valves) you should use additive.
Some people may notice that I have changed my tune a little, I used to say "suck it and see" and suggest that on a lottery basis some heads were OK and others not.
I've had my attitude adjusted by reading some studies on internal combustion engines generally and the effect of the change to unleaded on them. The really interesting thing was that for the first 10 years after some countries switched to unleaded some old engines had problems but the majority did not and initially nobody could fathom a reason for it.
It was the result of a number of variables:-
Firstly many engines turn out to need vastly less lead for valve seat protection than leaded fuel actually contained.
Secondly, the "new" unleaded fuel was transported, stored and delivered over the same infrastructure that had in some cases been used for decades for leaded fuel.
It turns out that the lead deposited on the "infrastructure" was slowly dissolved into the unleaded fuel and that minute amount of lead was just about enough in a lot of cases to protect valve seats, particularly during the transition period when the same infrastructure could have leaded fuel in it one day and unleaded the next.
This "masking" effect accounts for the very, very long time it has taken for the true effects of the transition to unleaded fuel to be seen, it also accounts for the undeniable fact that some engines had trouble whilst others did not.
Your choices are pretty simple, based on the depth of your pocket, the laws of your country and you comfort with breaching them and how "lucky" you are.
The headline choice is of course that at next top end rebuild have "unleaded" seats fitted - not a cheap process - the machinist will first run a bead of weld around the existing seat and see if they can drive it out. If they can, and the valve seat bore remains within spec, they will then drive the new seat in and then after renewing the valve guide will cut the seat and fit a new valve.
But if the valve seat bore is out of spec, or the machine shop has to "dig out" the seat, they will then have to weld up the head and machine a new seat bore, drive in the seat and then do the rest of the work - not cheap!
Option No.2 is to add the law compliant additive of your choice in the proportion required by the manufacturer. It is worth while to do research as whilst some additives have science behind them, others are mere snake oil.
Option No.3, if your country still supplied leaded fuel for piston engine aircraft then buy a 20lt drum of that and add some of it to your tank of fuel. In Australia we have diminishing availability of 100LL Avgas which stand for 100 octane, Low Lead. The Low Lead part is a laugh as 100LL has 4 times as much lead in it as leaded fuel ever did here. If you use 100LL in your R65 the ends fo the pipes will have a really nice white coating on them after 100km on the highway, that coating is pure, unburnt lead. Anyway, the people who claim to know such stuff say that 250ml of 100LL into 20lt of unleaded fuel every 2nd or 3rd tankful will maintain protection of the exhaust valve seats. The is the minor drawback that doing this is utterly illegal, not only from the standpoint of emissions but also from the standpoint that you have not paid the correct duty/excise on the Avgas. A matter for you and your conscience.
Option No.4, with due deference to those of the Catholic faith, I term "the rhythm method". using this method you check your valve clearances regularly and if you notice them suddenly start to close up, you have a change of faith and adopt one of options 1 through 3. If you are lucky and have adjustment left, your might avoid option No.1.
The problem is exacerbated by the fact that we simply do not know what POs of our heads have done to them. In my case I have a set of small valve heads that have been heavily ported and flowed and have had large valves fitted. I suspect that lead free seats were fitted, but there is absolutely no way for me to know - I use additive.
The Wife's R65/80 used to have 1987 heads on it - they were fine on unleaded. Sadly they had to be destroyed to recover the stainless steel headers, I do not know what year model the heads now fitted came from (I could find out but have not bothered), she now uses additive. I am layign in a stock of R65/80/100 heads as and when availability and finances permit, they will all have unleaded seats fitted and will be used next time.
