Rheem water heater gas valve issue
I have a Rheem 40 gallon powervent gas water heater (model# 21VP40E-1). This morning we had no hot water. The powervent fan runs. About every 5 minutes or so, the igniter clicks a bunch, and has a good flame by the burner plate, but the burner plate will not ignite, and after about a minute, the pilot flame goes out. It will go through this cycle a few times, and then suddenly after several tries, the burner plate finally ignites, and heats the water. When the burner plate ignites successfully, I can hear the gas control valve "click" and then the burner plate will ignite. When the burner plate fails to ignite, I don't hear the gas valve click.
I talked to a guy at a water heater parts store, and he said he is 80% sure it's the gas control valve. I'm thinking of just buying it and taking the chance that's the issue. The price is $135.
My question is, how hard is this replace? It looks like it's 3 gas fittings (main line, burner tube, and igniter tube. I'm assuming I just need to put thread sealer (tape) on all of the fittings. Besides that, is it just a couple mounting bolts?
Any advice would be appreciated!