I have to jump in on this,
with all due respect I would discourage:
Just remove it entirely from the casing and give it a good spray with WD40.
Also spray it in the cable hole itself and every part that moves.
The intent is good but..........
The WD40 method may give immediate results but you'll be creating bigger issues.
There are 2 concerns when servicing the Tach. and Speed. The "Hair-Springs" that return the needles to "0" are the VERY delicate and Sensitive !!!!
The residual WD40 will coat every part and this will attract dust. Of equal concern - due to the wording of the previous post - the WD40 will migrate into the counter wheels of the odometer and you do not want to have to remove and dissemble that !
Do NOT use compressed air - Any PSI will potentially destroy the hair springs !
Once the chassis' of the instrument have been removed caution must be observed regarding the Needles and the hair-springs ! I suggest using a small FINE artist type paint brush with (to be on the safe side) alcohol, to clean the dried lube from magnetic couplings. Slow needle response is a usually a result of dried lube in their bearing stems. Do this and any cleaning with the instrument face UP, so nothing runs onto the face plate, the hair-spring or the odometer wheels.
There is NO need to lube anything other then the cable input shaftt. There is no "load" or weight on any of the components and they are best left clean and dry !
There was a suggestion made some time ago, to free-up a slow-to-respond speedometer by removing the Trip Reset knob and spraying WD40 through that hole. Need I say more ?
Don't mean to rain on anyone's Parade - just trying to avoid someone getting caught in the proverbial Thunder Storm !