Thanks, Vince. I'm not pulling the heads as I have no way to properly re-align them. They will stay. I'll try other cleaners and then ignore the problem.
realigning properly is another point I didn't mention (or that I had taken for granted)... anyways, if the head has the simple 2 screws plate where one screw is fixed and only the azimuth screw is spring loaded, the head height and tilt angle are just automatic and, since the holes on the head plate are always slightly larger than the screws so that you have some play, you only have to get the head horizontal, at the right left-right place and set the right penetration, which is easier to do with a gauge but it's not impossible to do it without and, last, you have to align the azimuth as usual with a test tape.
But if the head plate has 3 screws, they all would be spring loaded, then without an alignment gauge it's simply impossible to get it right on anything.
point is that kind of corrosion might be nicely removed only "mechanically", then with something abrasive which polishes the head surface...
or, more simply, wait for the tape to slowly do this kind of work on the tape-head contact zone, which is the easiest and safest option... after all, outside of the tape-head contact zone, the problem is only cosmetic and it won't affect the performance.
Go figure... lately, I happened to replace heads on a couple 2-heads decks, then heads with 2-screws plate with only the azimuth one spring loaded, but the replacement heads (being NOS but VEEERY old) had different mounting geometry and I had to enlarge the hole and the slot on the head plate, otherwise it was placed just wrongly... of course, without an alignment gauge it was difficult to realize the head was out of place and impossible to place it right, especially after working on the head plate and then getting huge plays with the screws... so, it you happen to have to work on heads more times, a gauge is just a must have tool.
