Wow, those parts still have paint on them. Mine were nothing but rust

It sure has Juiceman. I get busy on it then the work drops off as I focus on other things. Where I currently am at with the 5U is putting the track frames back together, and I have new D3 rollers for it. I'm now debating whether to put series 1 D3 sprockets on it along with the appropriate rails since it seems the price would be not much different, at least the last time I looked. A new set of Berco D2 rails would be simpler of course. The 3J engine has been sitting in my garage for years - the cylinder head has been refurbished (new valves, guides, seats, and a surfacing) and I have a new set of liners for it (can't remember if I have pistons and rings) while the rear end is sitting out in the pasture. Inertia on those projects is endemic around here : ) My buddy with the D4 Traxcavator is pushing me to finish the 5U at least because he wants to clean out his pond and since I told him he is guaranteed to get stuck, we need something else to help pull it out : ) I'll need more than the current slicks that are on the 5U to get any grip though that's for sure. I think I'm going to farm that welding out so it actually gets done

Yes change them - after oil, replacing bearings is the next best maintenance item. Bearings are cheap compared to catastrophic failure