Jacuzzi TRI - clops locking ring problem

[jmcst25]

I have a Jacuzzi Tri - CLOPS filter -- The outer ring should easily come off - but I have to use alot of muscle to get it off - even after draining and opening the system to let air in.

Any suggestions on cause and resolution?

Here a picture http://www.poolcenter.com/parts_filter_jacuzzi_triclops.htm

#7 is the problem