I use PTFE lubricant on the linear bearings and white lithium grease on the Z screws, not too much though.
WD40 do a specialist lubricant range, but dont just use standard WD40 whatever you do! I just give them a light spray from time to time and wipe off any that looks dirty.
I have 2 i3 MEGA's printing about 14 hours a day churning parts out, one is the old original one with the buildtek type surface and one is the new type with the ultrabase, I just give them a wipe with IPA occasionally, the ultrabase needs very little cleaning compared to the buildtek type one, probably because you just lift the parts off where with the old buildtek type surface the prints stick like weld with no heat, so that surface requires a scraper.
Just as a side note, and touching wood, although both are constantly printing and run through kilo after kilo of filament, neither has had any replacement parts, and both are still running sweet (apart from the buildtek surface that needs replacing), neither has been modded at all apart from me cutting the tube free from the wiring loom and the deflector clipping on the gantry.
The first thing I did with the second printer before printing anything was wipe off the lubricant already on the linear bearings and apply ptfe lubricant, because, whatever they put on the first printer made the linear bearings a bit noisy, applying ptfe lubricant smoothed them right out.
ENVIRONMENT AND MACHINE TEMP SETTINGSThe temperature in the room where your machine is will have an effect on part adhession, especially if it has changed drastically.
Keep track of the temperature setting on your machine, as well as your room, that give you best results. Record this or write it and tape it to your machine in plain view so you can adjust as required for consistent results.