I rent a residence. Part of the agreement is that I pay all utilities and any repairs over $125.
I on my own paid the oil company $100 for a service contract. This entitles me to a year of free service for most problems.
The oil company came once to fix an oil leak. they said that without the service contract the repairs would have cost $400. Can I charge my landlord for the $400 repair? I bought the service contract on my own for convenience. If I wouldn’t have bought it then I would have had to pay the full price.
If I can’t ask for the $400, can I at least charge for the $100 service contract fee?
You cannot charge the landlord $400. You didn’t pay this, and they didn’t charge it, so you can’t pass it on. Even the $100 fee can’t be passed on, because you paid on your own volition, and it moreover falls into the “under $115” bracket.
Although it is true that by paying the money you saved the landlord a large expense, this is not a direct benefit (but rather indirect), and he cannot be charged for it. It also doesn’t fit the category of mishtarshi ley (see Tosafos, Bava Kama 101a).
However, you can certainly inform him of the circumstance, and perhaps he will be happy to refund you the payment.