Thanks for the prompt replies. As many of you have surmised, I'm pretty sure the age of the belts is the issue. It's very humid here on the windward side of the Big Island. I went through the entire stack of old belts, some of these were in unused condition right out of the box. Probably went through 10 of them getting the project I'm working on done. Many didn't last more than a few seconds. Frustrating. The last one I tried lasted quite awhile, long enough to finish the sanding, that supports the idea that the belts are the problem, not the machine. Thanks for the linked video woodnthings, I've attempted to repair some belts unsuccessfully in the past, but I'll check it out.
Yeah, I've been using this beast since I was a kid (I'm 66). I think it destroyed my Dad's hearing, he loved it and never wore ear plugs or muffs. I believe it has more power than my table saw. In my twenties I came very close to an unintentional sex change when I absently let it dangle too near my shorts as it was spinning down. Fortunately, it was just low enough that when it wound the front of my shorts into the drive wheel, only the skin of my thigh followed. Still hurt like heck, and left a spectacular bruise. Close call.
Rebuilt it a few years ago, new brass worm gear and sprocket, new drive wheel... Quite an undertaking, I was lucky to find most of the required parts. But it's still hanging on. Heavy machine for an old man. The depicted sander is an internet photo Kiwi, mine is the same model, but decidedly more shopworn. I dropped it some time ago and broke the plastic front Handle. Couldn't find a replacement as I recall, so I turned a new one (out of Brazilian cherry I think) on my drill press. Works fine and looks kinda' cool.