Hi Steve.
Thank you for coming back to us with your memory findings, I just went over the photo's of the last hydramount I changed for a member, I could not see any stamping of a letter on the one taken out and the one put in it's place.
maybe if I had took more notice of the base then I would have recorded it, I am sure we will find out sooner or later.
When you first said about the coloured dots on the mount I thought I have never ever seen any? and if they are on the 25/45 models then that is why.
As you can see from the photo's below I doubt if the old mount I took off the car I would have seen anything from the mess of it
Arctic