One thing that used to be done when I was doing refurbishment work of used fork trucks, was the machine was inspected, parts ordered that went in a box, then when you were given the job, you got the truck, box of bits and got on with it, there would be a tag on the truck with a job number, same number on the parts box and a corresponding job sheet, would a similar system be worth implementing so that any needed parts were in the box, making it a bit more efficient and the job sheet goes to the bikes new owner on purchase, a copy stays with you for warranty purposes, however it may be no good if you are wanting the clients to be able fault find and make decisions to repair or replace an item, but just a thought that may be helpful