A Cherry G81 series keyboard is hardly pure joy to type on, which is rooted in
a) the linear, steeply rising force displacement characteristic with forces of up to 100 cN
and
b) some friction between the mechanism's slider and its casing and the resulting roughness especially with off-center keypresses, which tends to increase the number of missed keys.
While there is not much one can do about (a), this is absolutely possible for (b). I used some silicone spray, which is plastics friendly, nonconductive and non-gumming. The supplied small plastic tube will be needed, and the dispenser should allow very small doses.
The mod itself is somewhat laborious (an hour maybe) but rather straightforward:
Open case, take off keycaps, with some extra care for the stabilized ones (inspect the mechanism closely so you can get things back together).
For each key mechanism, push down stem, apply a small squirt of silicone spray in all four corners, check sound of stem operation (should be smoother and damped, else apply some more), wipe off excess, proceed to next one. Use a bit only really, no flooding of the mechanism please.
Replace keycaps, checking for keys that still need some more lube.
Close case.
The result should be a smoother-feeling, quieter G81. It still won't be pure joy to type on, but the number of missed keypresses due to off-center strikes should be reduced. Ultimately this should allow for reduced force levels and increased typing comfort.
After first experiments with a mostly dead parts donor board, I applied this treatment to a 1992 vintage OEM (Peacock) G81-3004HAD. This seems to have taken it well so far, especially the keys which had already seen a good bit of use (and thus wear) in its life.
Please note: This mod has not been tested in the long term, therefore it can't be said whether some of the silicone stuff might want to creep between the membranes and mess up the contacts in the long run. If you don't feel comfortable with that, wait for as long as you deem appropriate and check back for whether my guinea pig board is still working.