1974 Shortcoming: Dashboard Instruments?

We just bought a 1974 280C from the second owner.
Jack, reluctantly sold his "baby", because, now entering his late 70's, hip replacements have made entering and sitting painful for him. He broke the map pocket on the driver's side swinging his legs into the seat.
The speedometer's 76000 miles appear to be reasonably accurate... tires mounted in 2001 were recorded @ 71000mi (and there aren't that many miles to drive on a small island like this one), etc. He has kept the coupe immaculate.
Is the dashboard instrumentation a weaklink on the W114?
The VDO quartz clock is non-functioning. Jack velcro-attached a tiny digital clock to keep time.
The speedometer needle functions road speed, but the odometer and tripmeter do not register. Resetting the trip numerals through to zero triggers the last number of the odometer.
The oil pressure goes to the 45psi maximum on starting and will stay there while driving. Idling, the psi drop to 30 or so & then return to 45 on acceleration.
What M-B engineering/design problems should we concern ourselves with? Can the speeedometer be wornout at 76K miles?
Is there any set order that these problems should be tackled in?
Are the M-Source booklets sufficient to attempt DIY repair(s)?
Anyone out there that has gone through similar circumstances...
My thanks,
Larry

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