I saw an add in our local newspaper: Project! R25 for sale, $1800.
It looked very interesting and yesterday I contacted the seller to have a look:

Do not let the "dirty" look fool you, it is rust protection, and behind that, there is very little corrosion. The seller bought the bike 35 years ago for his 11 year old son and it has been standing in his barn for 30 years.
As the seller himself likes to dabble with old bikes:

(this beautiful BSA is just one of several very nice, old bikes in his barn) I am rather confident, that the R25 is in a workable state, ie the seller is trustworthy.
The decision was easy and he took my offer of $1500, so now I am the proud owner of a bike only 5 (five) years younger than myself
greetings from a sunny/cloudy north where spring has just begun (we reached a staggering 59F in the weekend)