Yours may have the not so common twin-walled expansion tank where I think the bag is held between the inner and outer walls.
Pinched off Briskoda..
Removed a double walled mit silikat tank (part number ends in a ) and replaced it with a new M which is without along with mixing up fresh g13 to replace the old that was removed.
few interesting points...
That A suffix tank has a silicate container and a second mesh outside when I cut the old tank open.
The outer was intact, but the inner mesh was starting to degrade allowing a few crystals between the meshes, but still trapped safely.
The old tank has sensor prongs covered in plastic, the new just metal.
The tea bag style bags, it looks to me as if coolant movement could potentially catch the bag on these relatively fine prongs allowing them to damage the bag. Possibly the start of the problem.
either way, I think the older tanks are probably a safer design, but not infallible. The newer tea bag tanks seem like a bean counter design that’s backfired.
The basic M revision tank and replacing coolant at every water pump change is probably better for cars out of warranty. Changing coolant more frequently, eg every 2-3 years along with brake fluid would probably be good for additional piece of mind.
