I replaced the tank to toilet kit, bolts, gaskets and all, but I still have a leak. The tank simply is not sitting properly on the toilet. Any suggestions?

About 1 1/2 yrs ogo, I purchased an older home probably built in the 60s. Within the last 6 months, my tub has started peeling. Apparently, the ceramic tub and tile shower was coated with some type of material improperly. I have been unable to find out the type of coating that was applied and if this was done professionally or a do-it-yourself project(former owner loved to do home projects). The tub peels more each day and of course looks atrocious. I know there are companies in the market that will install bathtub liners. Does anyone have any suggestions and recommendations on what my options are here? I have to get this fixed as I am tired of looking at this mess. Thanks for your help.