Plumbing suggestions

I have a couple of plumbing questions, different but related. The first concerns the cup floor drain in my basement. It is of a type that has a plastic ball below a retainer ring that is supposed to float and block vapor travel to the basement. That ball is now somewhat damaged (no longer perfectly spherical). My house is about 25 years old and the whole assembly appears to be cast iron. The retaining ring is rusted in and I am looking for the best techniques for breaking it loose without completely breaking it. There are a couple of notches in that ring to aid in getting it started but it refuses to budge. Any thoughts on this? I assume that if I could get the retaining ring out, I could remove the ball and replace with some newer type of all polymeric vapor trap by screwing it into the basic cast cup.
The second question is similar. Between my bathroom drain in the basement and the main sewer line there is a cleanout in the concrete floor. I believe it is a cast iron collar with a metallic plate closing it off. I don't know what the plate is made out of. May be cast iron or steel and has a cross-hatch pattern on the top. It appears to be held on with a single slotted screw at one edge. I have had no luck attempting to remove the screw. Should I try Liquid Wrench, heat with a torch or heat gun or drill it an attempt to use an easy out. Looking for suggestions. Again, I would like to check to see if the area under the cover is clear. A retired plumber friend of mine said it may be a "flapper" valve under and if so, I would like to check it to see that it moves freely.
Bob Daun

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