Shower thermostatic valve o rings

[DIYspanner]

I've removed and cleaned out the valve.

I noticed that rear gauze filter is able to slide to and fro slightly and touch the rear o ring.

I've looked at a similar valve and it has additional o ring that keeps the gauze in place.

The shower has been working well but will the additional o ring to hold the gauze filter in place be beneficial?
In my opinion, it should be square section o ring.

 

[Burnerman]

Does the gauze ever come clear from the mixing ports, Mr. S?
Just to let any crap through, if any?
If the gauze doesn't move too far, I'd not worry about it - just reassemble with silicone grease when you're done.
John

 

[DIYspanner]

I've been in the house for getting on 2 years which was built in 2003/04. Has worked well enough till now. As you say John, grease up, install and carry on. I took the valve out because it was stuck albeit at a warm enough position. When I took it out, the gauze filters looked clean enough.

If any crap gets through, it'll accumulate in the shower head most likely which I can clean out.