Triton SM 20-3 backflush filter, which parts wear most often

[shellsingleton]

My main problem is a slight trickle out of the exhaust when running, which I believe allows suction to pull air in after the pump turns off as the filter drains down to pool level.
The nylon(?) washer under the handle is shot, and handle does not seem to want to allow the spring to pull it down into a fuly locked position. This may be due to debris(washer pieces?). I will pull apart the handle this evening to see whether I can fix it by cleaning the debris out.
If not, then I need to buy rebuild parts. I've read that the spider will allow suction leaks, so that is on my list for sure.
Which of the other small parts listed on this diagram are most prone to failure? I have a side mounted valve, not top mounted. I would prefer not to replace the entire "Top Valve Assembly" (#1), unless the parts I need start approaching that figure. Thanks alot, Shell

 

[shellsingleton]

After taking the cover off, it's apparent that the most likely culprit is the spider. basically everything else looks like it will either work or be broken. The gasket is noticeably worn also.
Just found a replacement at my LPS. Will report back this evening with the results.

 

[shellsingleton]

Got it changed, no leaks now.
Used "Lube Tube" with PTFE, and sanded the sealing suface with 1500 grit wet paper. Nice and slick.
Does the plunger usually stick up when you install a fresh gasket?
I had it installed upside down originally, my old one was so worn that the sealing ridges were gone.
It fit much easier with the ridges up, but the plunger is up, handle down and loose. I'm hoping spring tension will help the spider take a seat overnight.

 

[shellsingleton]

New gasket just tore. For future searchers... it is not ok for the plunger to be stuck in the up position when you finish installing it. It should be operable just like it was before. Not sure what I did wrong, going to start a new thread.