It may depends on the amount of the expenditure, and what, if any, elections or decisions the client has made regarding complying with IRS reg.  1.263 (a) 1

If they have been using the Mileage Allowance, it already has a maintenance, wear-and-tear component in the allowance, since it is for operating costs. You stated "large truck" but not "specialty vehicle." Details matter.

Doubtful that a large truck owned by a nonprofit organization would use the mileage method.

We don't know if "large" is a 3/4 ton or Semi or moving box van. We don't know if "motor" is $1,800 or $18,000.

Oh, there is so much we don't know...