Hi Patrtick. Here's a diagram showing both types of rubber bushings. I have #3 on my '53 that is more spongy than the harder #4 type. #3 was used up to chassis number 102285. Yes, these will both wear down and if exposed to oil, they will deteriorate, causing excess vibrations. A worn roller bearing will be quite noticable, producing a grinding noise at all speeds. I do have a few spare sets of #3 if you cannot find them elsewhere.