If it ain't broke, if it is still working - leave it alone ￼
Not quite! Old, lacquer-potted windings are susceptible to cracking, damp-ingress and eventual breakdown....but unusual in anything under 30 years old .
Modern Epoxy-potting is "fit and forget "
A hypodermic syringe can be used to lubricate ballraces NOTE 1/3 full MAX.
Sliprings usually have a brass contact-pad and sometimes this wears at a different rate to the rest of the (plastic) ring. Skimming the surface to remove any step will lengthen the life of the contact-brush, which will, in turn, reduce carbon-dust and the possibility of tracking and shorting.
POINTS ! they wear, the "heel" that rides the cam wears. Normally, there's a grease-soaked pad that should lubricate the cam........it takes a "set" sometimes it's possible to turn it over and then the bend actually improves the pressure.
The points themselves are normally a tungsten facing on a small post.....one will ALWAYS build a lump, the other a crater (DC current,tiny spark every time they open, think arc-welder)
Polish with a whetstone / wet and dry paper (600 grit is OK) a magneto/Swiss/Warding file may be needed first , to reduce the "pip" .
The "gap" is absolutely critical for optimum performance, as it determines at what point in the armature's rotation, the optimum flux-collapse occurs. The timing of the magnetic "break " is part and parcel of this.
I suspect a lot of Mag troubles are caused by poor points-maintenance.
Lastly, the capacitor...they're cheap, they quench the spark at the points, thus lengthening their life and preserving timing. The quenching also ensures a much quicker collapse of the primary-winding current. - this, in turn, gives a stronger induction into the secondary-winding = a fatter spark!
There's plenty of info "on the net" for those seriously interested.
by and large this "dump or overhaul " business, strikes me as a total con-trick.
Bead-blasting and painting are purely cosmetic. the major issues are points and bearings...they're the wearing bits.
If dismantling, be aware some designs have paper insulators around the armature- bearings. they must be in place and intact!