Tair-3 Phs - cleaning rear elements?

[BigMackCam]

I have a Tair-3 Phs with dirty elements. I've managed to remove the optical block from the main body, and I've removed the front element, cleaned that successfully, and replaced it. But I'm having trouble getting at the rear element(s) and I'm not sure how to gain access. Set down inside the barrel is a very, very tight retaining ring. I can just about move it with a lens wrench, but there's a lot of thread in the barrel and I want to make sure I'm doing the right thing before I go ahead and remove it.

Does anyone have any experience of cleaning the rear glass on the Tair-3 models? I would be very grateful for some pointers!

Many thanks in advance

[BigMackCam]

UPDATE - no need for replies... I was able to remove the retaining ring. It just took a lot of effort - the threads were very dry and probably a bit grubby too. The rear element came out fine and has cleaned up just as well as the front. The lens is back together and working fine now