I just replaced the original accessory drive belt on our 96 SW1. The belt had not failed and displayed no adverse symptoms or noise but it was just so old (244,000 km) that I couldn't stand it anymore. It is difficult to inspect properly without removal and I had never done this. Once I got the old one off it seemed like false economy to reinstall it so I placed it around the small spare tire (perfect fit) to carry as a spare.
The old belt showed the even cross cracking that I anticipated but there was no missing segments and the cracks were not down to the fabric. The belt did show very small gravel imbedded in the belt grooves and the crank pulley also had very small gravel jammed in the grooves. The other pulleys had clean grooves. I started the engine with no belt and used a (long) straight blade screwdriver to clean and scrape the gravel from the pulley grooves. USE EXTREME CAUTION
I think this belt would have lasted a lot longer but it was a good candidate for preventive maintenance as when it finally failed it would probably happen in the cold, dark and rain. It will still be a good emergency spare. New belt $20, time