the oil pressure sender cost:
VDO 70$ plus(fastlane)
Hamburgtech $30(mercedes autohauz)

Where/when did you get your 35$ sender from?
Is the $35 price 10 years ago?

I have the same problem,the car worked for 6 months now,
last week passed emission test with one-tenth of limits.Must not have been anything lethal to the engine!
So I have time for some research on senders and found the above prices.Oe Vdo would definitely be more than $35.

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Tom 2010 C250 4-matic Sport (Canada)