Why not put both dates on the invoice, one for the quote and the other for the work completed, 2 birds with 1 stone so to speak.That way the previous owner can see the problem was reported early doors.
I'm not at all familiar with your machine but strange faults like the one you mention are often attributed to the electrical/electronics,causes such as internal water leaks, quality of the electrical supply or damage caused by transient voltages, (spikes) etc to name a few. Is the programmer...
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