I too have been down the "learn from experience" track, I too have learnt that the "element" dissolves in a caustic solution. I too have found that I was unable to totally clean an "element" after bead blasting it.
The air filter that I "dissolved" was from a Ford Prefect and the one that I filled full of glass was from a 36 Ford.
In both cases I was able to get a replacement air filter.
If I were to need to clean an oil bath "element" today, I would ensure that the "element" is totally free from oil and have it soda blasted. This way the bi carb soda is dissolvable, ensuring that no contaminants remain in the "element". I would also ensure that as much of the "element" would be covered as possible to ensure that any rust or paint did not lodge in the "element".
Maybe it would be better to obtain a replacement air cleaner lid with new element. I realise there is the pain of having to redo the lid in two pack to ensure that it matches the base, it sounds like you have done a great job on your car and, like you, I would not be taking the chance of particles coming out and getting into the engine.
Keith