Needed a pair of these for my 912 , nobody does them in the original style rubber . You can get Solid mounts or hard rubber mounts .

These are used on the 901 and 902 Gearboxes . (This mount is usually used on the early models 1965/66/67) These rubbers fit into the

901-375-031-00 Gearbox cradles . 

These can be pressed into the cradle with a little silicone lube and i used a small press . (See image of cranked tool I used , it is a bent piece of 12mm / 1/2inch studding with a stop nut , this tilts the mount over and makes fitting a lot easier than just pushing square on , I used a squirt of silicone spray , the rubbers have a slightly smaller diameter on one side I press this side into hole)

I recommend changing both at the same time .

NOTE , JUST RUBBER MOUNTS , NOT THE CRADLE ..........