OK, I have spoken with Nikon and they couldn't offer any option/advice other than to return it to them once again.
As it's less than a month since they sent it back to me after the previous service, they are going to e-mail me a pre-paid UPS label so that I don't incur any shipping charges.
Apparently, I can't ask for a rapid turnaround until I have the new Service Order No. which, of course, I won't receive until they have opened up the package and read my cover letter. Damn! This means that I'll probably be without it for a total of around 3 weeks again!