I don't want to question why you feel it needs retirement or replacement (that's up to you) but most tanks (especially Tamiya) only need parts replaced or upgraded to bring them back to life and since you're wanting to stay with a Pershing and not another tank.

You could always sell it with a list of things it needs to help finance another project?

Or, change that M26 into another version/model if you're bored of that one.