RV Repair: removing vent, rubber roof sealant, tacky tape

Question
I am having trouble removing an old vent in the bathroom. I have a 1978 Layton I just bought it and the bathroom vent leaks. I would replace just the lid, but have already bought the whole thing. Now I can't get the old one out, it appears there is some sort of stuff covering the screws on the roof and it is very hard so I can't remove it. Any suggestions???
Thanks,
Christy

Answer
This is a job you MUST do right. You have to carefully scrap off the old sealant and expose the screws..then carefully remove the screws and vent. When you replace it with the new one you must put Tacky tape around the under side of the vent. Install the vent. And seal it with the proper sealant. Fiberglass sealant or rubber roof sealant....Whichever you have. Good Luck.