1987 rheem: How to change ignitor

Ok this is a 1987 RHEEM dual unit on the roof. I was told that the ignitor was bad. Here are a couple pics to give ideas of what this all looks like.







First> I was able to undo the rather small assembly that the ignitor is in but can't get it removed. I see no retaining ring or anything holding it in place. QUESTION.. Is this something that I can just take some sand paper to and clean it up and will it work again or would it actually need to be replaced ?