My 1985 300CD-T (Calif.), 30+ years old now (203,000 miles), still uses the original starter and neutral safety switch.

My question: Is it advisable to replace these two items prior to their inevitable failure? I intend to keep the vehicle for the foreseeable future.

Starter background...as of now:
A) The starter motor always turns over but to my ears, it does sound a bit like it is getting tired (3 year old Interstate battery in use).

B) There is no trouble with the starter slipping or grinding-screeching during cranking.

C) I have not noticed any starter solenoid clicking or lack of clicking.

I have replaced the starter on a 300D and so I know the work that is involved. In that case, I replaced the starter at 232,000 mi. not because it failed but because a professional M-B Tech. told me: Since you have the intake and exhaust manifolds removed for the head gasket and head replacement you're doing, it is an optimal time to replace the starter.

I am aware that, among other causes, when the tips of the starter drive wear, the timing between pull in slow rotation and full power rotating becomes incorrect and causes the starter drive to rotate at full power and impact the flywheel teeth. Translation: Fatiguing the teeth causes them to break.

So, regarding the starter...
Any thoughts about the wisdom or foolishness of replacing the starter and solenoid before either or both clearly show signs of impending failure or just quit?

Same thing goes for the neutral safety switch:
Replace it before its death is known or just let it die a natural death?

Thank ya-