Okay a quick update - I thought I would try something really simple (and dumb) before going to bed. After I identified what I think is the CR encoder strip (long transparent tape), I used a square of tissue paper to gently wipe along the length and dislodge any dust particles that may be there and restarted the printer. Unbelievably, that fixed the problem! So far it seems to be none the worse for the wear; after a quick head cleaning cycle, almost none of the heads are clogged.
I'm still keeping my fingers crossed, but I'm hoping it was just dust on the encoder strip that caused this problem.
Thanks again Aaron for giving me the push to try and fix it by myself :-) I'm really impressed with the 9800 - I guess it does indeed deserve its reputation.
So, for future reference: if you see error codes 0010007 and/or 001001D, try cleaning the encoder strip first before trying more expensive options.
Anil
Thanks Aaron, I will give it a shot. I do have the service manual (the one for the 9800 seems to be freely available online).
Anil