Degreaser and oil recommendations for Nexus 8
Don't use degreaser on the insides of an IGH! Not! Ever!

For Shimano Nexus/Alfine you are supposed to use the same oil for cleaning and lubrication.

For Rohloff there is a separate cleaning oil which I think has lower viscosity than the lubrication oil.

Also you replace the oil at most once a year or every 5000km, not more often. Some hubs might need their very first oil change earlier, like after 1000km.

This assumes going though the bleeds nipples like normal people.

If you are going to take the hub apart completely (not just remove the gear block from the housing) this doesn't necessarily apply, but taking the hub apart is not something even good bicycle mechanics do. It never makes economic sense. If taking it apart and fixing it is cheaper to you than having it replaced, then it didn't make economic sense to buy it in the first place and you should have gone with something cheaper, simpler, more mechanically elegant and more maintenance intensive - as in, much less maintenance than taking apart and fixing an IGH.