Leaking Bathroom Sink

Own a 2006 Fleetwood Bounder 35E Class A MH. Rear bathroom sink was not draining well. I took it completely apart and cleaned out the gunk in the drain tube and P-trap. I'm a little familiar with home sink repairs, so knew I would need plumber's putty. However, the "putty" that was there was very, very sticky. I had to use a solvent to get everything cleaned up. This had me worried. I pressed on with "regular" plumber's putty. After a few weeks of having a dry paper towel under the P-trap, I thought I was golden. Then a leak started. it is coming from where the drain and the sink connect. Took it apart and it looks like the plumber's putty was, I wouldn't say dissolving, but something like it. I cleaned everything up and prepared to redo the plumbers putty. Read the container. Says not to use on plastic components! Use Oatey Sillicone Sealant instead. Having an issue finding the recommended putty locally. Everything I'm working on is plastic!! Maybe that's why the previous stuff was very sticky. I don't know what that material is. Need your help identifying. Gonna use the normal stuff just so I can get the sink operational. Will have to redo once I get the "correct" stuff.