Not yet, but I would be having a serious look at the 550 if I did.
Had a look at the 400 at the dealers today, very similar to the classic 500.
Nearly lost the engine of the 500 last time out on the property. I had changed the oil and filter the day before and my brother and I were heading a couple of Kms down the road to another paddock. One of the sheep dogs had followed my brothers quad and had pulled up lame. I stopped to pick him up and looked down to see my left boot covered in oil. Closer inspection showed that I hadn't tightened the filter enough and the O ring had squeezed out letting oil go everywhere. We towed it back to the shed, tightened the filter and refilled with 1.5Lt of oil (only holds 2.0Lt). Rest of day I kept looking at filter checking that it was still tight. Thanks to dopey dog I stopped in time, another 2-300 yds and it would have been a solid lump.