Clunk Once on each revolution of the tumbler - Rollers ?

Hi:
My old Whirlpool dryer makes a "Clunk" once on each revolution of the tumbler.
I’m guessing it’s the upper or lower roller…?
Felt the lower roller through the back, seems ok but can’t tell if the bearing is bad.
It’s getting loud.
Front seal seems a bit worn - small gap between the front seal and tumbler
but it seems to track or roll on it OK.
Rear seal seems OK.
Haven’t looked at the idler either.
Don’t have a service manual and can’t find one.
Thanks

Couple things I can think of:
I doubt it is a roller as they turn a number of times per drum revolution.
Unless one of them is not turning at all.
Check the seam on the drum where the rear rollers ride.
Check for a loose paddle in the drum.
Check the seals on the drum to be sure they are not snagging on anything when rotating

Here are your parts
http://www.appliancepartspros.com/partsearch/modelsearch.aspx?model=LER5636EQ1