Think it has to be a rubber grease, there is a special type. I ordered mine with the iso conversion kit. Some greases will disolve the rubber over a long period of time. Make sure the inside of the tube/mount is really nice and clean, grease the rubber donuts up good and the inside of the tube, and slowly, at an angle, get the first one started into the tube, the last bit, before it can turn so it is straight in the tube, will be the most difficult part, but it will go in, use a blunt instrument, to work/push it into the tube. Might be a good idea to place the tube , wrapped in clean rags, in the bench vise too, and use good gloves to protect your hands, to avoid offending the ears of the neighbours, when during pushing, things slip about and you wack your hand into the tube or something...just a suggestion :wink:
The second donut will be a bit more difficult, because, by then, it will have to go into the tube from a straight angle, but it WILL go in with a bit of concentrated effort :wink:
The donuts and tube have to be pushed far enough into the tube to get them pretty centered, ends looking just a bit out, or just a bit in, same amount. If I remember correctly, the front mount will be a bit difficult to get into the frame again, but it can be done, and the rear mount, can have all the parts exchanged without being removed from the frame, just support the frame/cradle etc properly, not sure it can be done with it on the center stand, but maybe.
One way or another, it will all work, and you will be perhaps very pleased with the results. Mine have been in now for 5-6 years, and that conversion, is the first, most important one I would be making to any bike I ever worked on, the future. From all the little changes I have made to my bike over the years...that one was the one that did the most to make it the pleasure it is today to drive. Nothing was worse, than those old, loose, crappy original iso setups...all they did, was teach my bike to Hula dance :wink:
May the gods of Norton repair, watch over your shoulder.....