Dave: Thanks for reporting back. Well done with the steradent treatment.
I have in the past, cleaned out screen washer bottles by chucking a handful of pea gravel in, with a cup of water and giving it a good swirl. Having not closely studied the baffle arrangement, would that work on the header tank or is it likely that either the gravel wouldn't reach all the parts…or if it did, it may be difficult to get it out again?
BTW, the comment from Keith about heater valves, I agree with, especially on +4 s from this era. Flaps are the only heat control.
