So when an SBC pump needs to be replaced (as opposed to the actuation counter simply needing to be reset), what is it exactly that fails? And will the likelihood of such failure be minimized by regular brake fluid replacement?

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 157k miles
06 E320 CDI "Rutherford", Black on Tan, 175k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 144k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 70k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

I would not be losing any sleep over it and just replace fluid every couple years.

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Jim

Not losing any sleep over it...just curious about the mechanics of the failure and if there's any meaningful correlation with not changing the fluid.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 157k miles
06 E320 CDI "Rutherford", Black on Tan, 175k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 144k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 70k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Excellent Q.

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'06 E320 CDI
'17 Corvette Stingray Vert

In general, I've noticed that changing brake fluid will do 2 things, pull moisture out of the system reducing rusting of steel components and fresh seal sweller additive keeps seals from leaking. ( and piston cups too. )

On my truck I had a master cylinder starting to leak internally causing the pedal to slowly drop under certain conditions. ( pushing the pedal very slowly especially on a bumpy road. ) As an experiment I changed the brake fluid and after some short period of time ( week or so ? ) the internal leakage stopped and the MC was fine for a few more years. When it started to drop again I replaced the MC.

Brake seal wear is very gradual and does not suddenly occur, it just takes the right conditions for the driver to be come aware of.

The only real way to tell what SBC component failed (and not timed out ) is to scan the computer when it shuts down. That data is difficult to come by outside of a MB shop ( not dealer as they tend to see only newer cars. )

Given the SBC is entirely electric powered, if the pump motor is a brush type I'd expect that the brushes wore out or motor windings failed. ( like an electric fuel pump motor wearing out ) I'd think the next levels would be the accumulator, random electronic component followed by an internal mechanical failure.

Mine had a white warning, i took it in and he read the code, it said, "Hydraulic fault pressure regulator right front wheel"
Code C22BC

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1959 Gravely LI, 1963 Gravely L8, 1973 Gravely C12
1982 380SL
1978 450 SEL 6.9 euro restoration at 63% and climbing
1987 300 D
2005 CDI European Delivery
2006 CDI Handed down to daughter
2007 GL CDI. Wifes