[vr4]

I have a gso 12" dobsonian that i havent used for about 18months. When i got it out and went to set it up i noticed a discolouration around the edge of the primary mirror. I cant tell if its some sort of mould or if the surface of the mirror is starting to deteriorate as the scope is about 4 or 5 years old.

The rest of the mirror has only has minor dust but has anyone else experienced something like this? Im trying to decide if its worth the risk of trying to clean it off or if i should just leave it. I havent been able to see if it affects viewing quality due to the cloud cover over the last few days. The photo makes the rest of the mirror look a lot dirtier than it actually is but it shows the ring around the edge that im concerned about.

Any advice appreciated.
Thanks