Caliper corrosion

Took off my front (Nissin) caliper for an overhaul as it has been sticking for a wee while and removed the pistons to find they were pretty corroded (and rusty) Managed to pretty much clean them up with a scotch-brite pad and elbow grease. Took out the seals and there is quite a lot of corrosion in the seal seats which is proving a real swine to get removed. The corrosion is difficult to see at some places and difficult to get to. I have tried to use brake cleaner but this doesn't help any. Had a thought about sonic cleaning - would this affect the painted finish? Any and all suggestions gratefully received. Almost cleaned up one set of seats but then had a look later and found more corrosion that I had missed

Sorry, posted this in the wrong section - not too sure how to move it across though.

You need some kind of 90-degree scraping tool to get the grot out of the seal-seats - like one of those ones the dentist uses (google 'dental picks' for a picture).

Even if you had one, you would still need to be careful not the scratch up the caliper - it is possible but care is needed!

I don't know if an ultrasonic cleaner would help (it probably would). I think the ultrasonic cleaner would only dislodge parts of the finish that were going to fall off anyway...

I've always found electrical screw drivers small and narrow enough to clean most of the crud out but just be gentle as you go and it should be fine.

Done this way for quite sometime (without a 90degree tool) and brakes have always worked without leaking afterwards.