How hard is it to rebuild a non-stuck caliper myself?

Its an original unit and all the seals are brittle.

I have had bad luck with purchasing rebuilt calipers, they make me nervous.

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car