I used silicone lube when I rebuilt mine! big up the perfectionists ^^
The lever assembly is dead easy to strip and rebuild, it's pretty much just the lever body, the lever, a spring, and the piston.
if this is your first time bleeding with water, you have to REALLY flush the buggers out. I stripped down my brakes entirely when I made the switch from oil to water. Gave everything a proper clean and lube before sticking it all back together and bleeding.
It's a fair bit of work, but I reckon it's worth it in the end, and by taking them apart you get rid of 99% of the oil in the system, making it quicker to flush when you get to bleeding