I recently pulled a 300D from 10yr storage , car was parked and left.

New battery , started right up with the old fuel, drove 500 miles home, fixed the perished rubber parts , etc , good car again.

Note , the diesel did not do off , and no alge growth, but the latter might have been good luck, not good management.

If you can get someone to start and moove the car each month , maybe your brother, just to make it look less derelict....

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'72 240D
'76 300D
'88 300sel
'40 Chev pickup , the shop hack.
'73 Monte Carlo Landau, for "Super Chevy Sunday"