Abbey SM50. It's basically molybdenum disulphide in a silicone oil base.
There is a way to adjust the sidewheel tension with the wheel off. I've done it on mine but it's fiddly and I can't now find the thread with the pictures on. It involves prising off the Nikko shield badge and that reveals a plate with two holes about an inch or so apart. You need a tool with lugs to fit in those holes to unscrew the plate. Some use a piece of wood with two nails hammered through and their ends filed off. I found a pair of circlip pliers worked quite well but was extremely fiddly. I also remember this plate has a reverse thread, clockwise to loosen. To just adjust the tension you screw in/out this plate. To get at the o-rings to lube them you unscrew it completely. I used silicone grease on the o-rings.
The last thing I remember is takes quite a few times to get the right tension. Too loose and initially it feels great, until you get the big wheel back on and try it out, and there's a bit of wobble in the wheel. Not much but enough to annoy me. The thing is it feels much stiffer without the big wheel on, obviously. So if it feels just right without the wheel it will be way too loose. Also this isn't for the hamfisted, it is possible to snap the sidewheel shaft apparently.
Hope this helps. If you spend a bit of time searching you might find some pictures on the interweb.
EDIT: I just read the post said MK3 Nikko. ALL THE ABOVE APPLIES TO MK2 NIKKOs. I've no idea about Mk.3 but it may be similar
Last edited by Adam; 3rd April 2015 at 12:51 PM.