Ok, here is all you need to do.
Take the bearing housing off of the unicycle, clean the bearings and the holder of any dirt and rust, or any other type of junk lodging its way in there.
Take off your cranks, clean the splines, and the splines of the cranks, and anything else that you can see needing cleaning. Do not use WD40, it is for water displacement, and not actually lubing the splines. Once you get the splines and everything cleaned and re-lubed/greased, set them back on but put them on at a different angle than before. This will be just the same as rotating your tire, but all you have to do is take off your cranks and move a few splines from the original position, then put them back on.
Having the cranks back on, in a different position from the original, tighten them up, and then put the wheel back into the frame, making sure the R crank is on the right, L crank on the left. Put on the bearing holders and tighten them up snug, but not too tight o you just be clamping down the bearing and they will stop spinning. Keep it tight, but still let the wheel spin pretty freely.
Re-tighten your cranks again, just for reinsurance. Now you got your uni back together, go through it and tighten the seat clamp, and the bolts under your seat, they could be loose.
Check your spokes and see if any of them need to be tightened.
Take your uni for a quick 10-30min ride, do lots of drops and gaps to see how the uni is holding up, take it back and and give everyone one list twist too make sure nothing came loose.