So I purchaed a carbon fibre C11 late last year to replace my Meade 12inch ACF which was just too much scope for me to manage. Scope looked in excellent condition overall and it was a decent (not amazing, but decent) price and local.
When collimating I noticed that not only did the fastar holder for the secondary move around, it moved up and down and side to side. thought that the holder must have come loose, I did eventually manage to remove the fastar ring, but there was no way to tighten the holder (even by shoving my hand in the opening) - so I then attempted to remove the corrector plate.
I've done this on serveral other SCT's so it didnt daught me - but the first thing I noticed was that the metal retaining ring wouldnt easily come off - after some effort I noticed that it appeared to be gummed up with some residue - looked carefully and saw that the material (foam or rubber?) was pretty hard and degraded - it had left a lot of crud on the corrector. It was also impossible to remove the plate - it was stuck on the other side by the same compressed foam/rubber. I added some IPA around the corrector and after letting it soak for 10 minutes the corrector popped off. Yay! I played around with the secondary holder attempting to tighten it to no avail - then I added some more IPA around the inside of it, and eventually the holder did tighten up, and now there is no play or movement.
So far so good - now the fun begins to clean the corrector. After about an hour of failure (I would clean, and find new residue finding it way to the surface) I realised that the corrector edge was covered in some sort of white paint or glue - this was the culprit - I then used cotton buds and various solvents to remove the white stuff, and after some effort got the corrector cleaned nicely.
I guess to the topic title - is it normal to have foam/rubber on the place the corrector sits in the OTA and is it normal to have a white glue/paint on the edge of the corrector? Both seem to have degraded. I dont believe this scope is super old. (mid 2010's I think)