Thanks for your help! That video was really useful. From watching it I realized, that silicon grease would not be optimal, so I ordered Krytox GPL 205 0.5oz. Pricey, but oh wow it feels awesome. Though after finishing with the whole procedure, I realized one other thing, and that is that the Topre keycaps don't fit on the JTK sliders
) So now I have a beautiful black HHKB with yellow JTK sliders, Hypersphere dampers and lubed with Krytox, but no keycaps to complete the build - rofl. Guess I'll have to shell this for a bit longer till a nice, HHKB-compatible set comes along, which turns out to be harder than anticipated.