What cleaner off-car/on a bench would be the best, e.g. Berryman B12 or just plain carburetor cleaner?
-> Plain. I use STP carb cleaner which is readily available at most parts shop and even supermarket. I have done it via Mike's method below:
https://www.mikeponte.net/volvo/injectors.htm

Usually a can of carb spray is enough to service all 4 injectors. Two cans if you wanna be super clean :)


Techron doesn't come in an aerosol spray can.
-> True. This is only to add into fuel tank. Good for occasional use to maintain injector cleanliness. About once or twice a year IME.

Amarin.