Sta Rite Heater Problem

Hello. I have a Sta-Rite natural gas heater (not sure if SRC 200,333 or 400) but have recently had an issue. At first, the heater wouldn’t kick in, the blower worked, checked back of panel and AFS light was on. So I cleaned out blower motor and taped up the blue wires, the AFS light went off. Then I fired up again, heater fired up this time, but after a few seconds, heard a lot of clanging and shaking. The temperature reading went up to 96, then declined rapidly down to current temperature while shutting off the heater, blower still ran. It seemed like it was going to continue cycling on and off like that so I turned it off and closed gas valve. I saw online someone had same issue and is was a broken manifold valve, would you agree that is the issue? Thank you.