As I am trying to  clean the remnants of the dissolved vibration filter in the tank I see a 4 - 6 inch rubber strip laying/glued? perpendicular to the bike frame in the forward bottom of the tank. I have not read anywhere or seen any pictures of this piece unless is part of the dissolved rubber vibration damper. I will attempt to post a picture.

I have not been on the forum much lately and I do not know where my picture went!!

Like these strips under discussion, Shep?

Thank you, yes. 
One strip under the fuel pump and the second one forward of the level switch assembly.
Still not sure that they help dampen vibration noise from the tank. As long as the strips don't disintegrate like the pump vibration damper did then I don 't care.
My 85 tank has no rubber strips.
Shep

I was guessing (so likely wrong) that it's not so much against vibration, but to allow the sides of the tank to expand and contract under different pressures and temperatures. If one part of the side of the tank was prevented from expanding, for example, but not the rest of it, the panel could develop a kink.

So mine have been the other way round... none in the '83 (LFB), none in the '85 (Brick2) but two in the '87 (Kostenlot). Go figure.

Dai, I might have not been as clear as I could be. No strips in the production year machine number 1984 July/(F0040448) but the strips are in the production year  number 1986 Dec/(H0142581).
So mine are more in line with your tanks and years. I never know when to post the production year which I believe to be accurate or the model year which I am never sure is accurate!