I guess we will need to rename this thread Grommetgate.

Hopefully you all will be pleased to know that yes, I stared at the same tables, consulted with people in the elastomer industry, and had testing done on original factory parts I bought in 1989. We worked with our supplier and selected a compound with the right qualities and durometer, based off the original. Even within a specific compound, there are several quality grades. We selected a high quality grade compound, probably better than what Rhodes originally used, but I cannot say for sure for obvious reasons (I wouldn't even know who to ask, and they probably wouldn't remember anyway). We may need to wait another 10-20 years to find out how the grommets hold up long term. I can say that our grommets have been in production since about 2008, they are in my personal instrument that had pancaked original grommets, and as of 2016 they still look great and function as intended. I doubt they will change appreciably in the next 5-10 years since they haven't changed yet.
If we didn't select the appropriate compound and durometer, it is unlikely voicing would even stay consistent on a given piano as the grommets would deform in a very short period. This is why we had grommets made in the first place (during the Keyboard Cottage years) because *every* Rhodes supplier at the time was selling McMaster or McMaster style grommets. They were often sold with flat head screws and captive finishing washers in most cases (as was in the Mk V). They NEVER fit properly and 2 hours after voicing the piano everything would be all over the place again. Playing the piano would also cause voicing to drift! I did not want pianos in the field doing this, so we decided to have grommets produced ourselves. It wasn't long after we released ours that original looking grommets became available from other sources.
Yes our grommets are more expensive. They are sourced here in the US, and made from high quality material. The fit and finish is superior. There are no deformities, flash, wrinkles, bubbles, etc. All our grommets are consistent, and we provide a few extras just in case.
Our screws are custom produced with the correct shoulder to fit in the grommet properly. Again, here in the US. We opted not to have them nickel plated to keep the price lower, as it is not an externally visible part. They are still plated, however, for rust and corrosion protection. Quality thick flat washers, finished the same as our screws, were also chosen.
At RetroLinear we do our best to do things the right way and put the effort where it really counts. This is why discerning clients keep returning to us. Our instruments feel great, sound great, and our parts and electronics are very reliable. And the end results are obvious, if you take the time to listen and compare.
Tim
retrolinear.com