My car is 23 years old and has about 75000 miles. From my reading good reliable suspension parts are getting hard to source.

When might I expect failure to begin?

Should I try to source good parts to have on hand? It appears good parts will become increasingly difficult to find.

It appears that most of the available new parts are not as good as the Mercedes original parts. Should I replace only when there is a failure or do all related parts at one time?

Is there a coating that can be sprayed/brushed on the rubber parts to reduce failure by age? It seems if road oil and ozone can be kept off the rubber the parts might last longer.

From my reading manufacturer parts seem to be best, then maybe lemforder, Meyle-HD. Any brands that can still be trusted to provide good service?