At a certain Mil station with a lot of specialist vehicles for different climates, they are happy to replace a driveshaft complete - at a cost of many thousands of pounds - when a £1 oil seal from Halfords would have cured the problem.
There's a solution, once mandated, which you learned long before ever being in MoD(PE).
1. Call up DefCon 112(Repair) in the contract.
2. When such a issue arises, the MoD QAR, or repair manager at the company, or in extremis the MoD project manager, having satisfied themselves that the proposed part is suitable, convenes a LERC (Local Equipment Repair Committee), in accordance with DGDQA Standing Instruction 0136. ('Standing Instruction' is the giveaway).
3. He says 'Buy it from Halfords for a quid. Meeting closed'.
4. Minutes of meeting are immediately contractually binding, and constitute a contract amendment.
MoD commercial preach what they are taught - only commercial can let a contract. Wrong, and this is one of many examples, all designed to maintain front line capability and safety. No doubt why the procedure is no longer used.