pedestal sink - leak between j bend and trap arm
we purchased a new faucet for our half bath that has a pedestal sink. the biggest challenge with this pedestal sink is that the pedestal isn't open all the way (think 2 holes with a bit of porcelain between), and the tailpipe slip nut is covered by that bit of porcelain (and no obvious way to tighten). so to get around this, i've decided to work on the plumbing without the pedestal. once i'm leak free, i'll disconnect after the ptrap and re-tighten there.
my problem is that there is always a leak between the j bend and trap arm. the tailipe is plastic (new), j bend is chrome (new), and trap arm (original) looks to be chrome. i've purchased a new j bend, and am using a nylon washer for the tailpipe. the reason i purchased the new j bend is that the original washer was all pitted and dried out. i couldn't find a new flat rubber washer (original), so i figured a new j bend with a rubber beveled washer would be best.
i can't tell much about the leak, but it does appear that it comes from the top of the slip nut on the trap arm. also, i'm not sure if the existing trap arm would be compatible with a beveled washer, but it seems to fit snug. i haven't used any goop, paste, mud, caulk, gunk, etc. and am not sure if i should.
any suggestions on what to try or do next? the only thing i'm worried about is that once the plumbing is leakfree, i'll need to disassemble to fit around the pedestal.
thanks for your help!