Thanks. I haven't changed the transmission oil yet, but I checked the level and the small amount of oil that came out when I removed the filler plug looked to be in pretty decent shape (not grey and metallic!).
Once I managed to get the sliders in the right way round, going from the rollers to the 6g sliders gave me about 5 mph in top speed (indicated 45 to indicated 50) and significantly better performance going up steep hills, so I'll probably keep them. It's worth it even if I have to replace the variator at some point. Whether I could have gotten the same performance increase with new rollers (the old ones had flat spots) I don't know. I'm using KOSO (Taiwan) sliders, which I think are pretty good quality.