I hate to be the bearer of mad news but as good as the PDR-W739 was as a recorder I think it will be near impossible to get the cd changer transport repairded. Contact Pioneer to see what they say.
It might be easier/less expensive to get another cd recorder. My friend has the PDR-W839 (the replacement for the W739, which I tried to find and buy but couldn't because they stopped making it in late 2002) and we used it as a reference to test run other cd recorders. I ended up with the TDK DA5900 and it has been great. Can't tell burned cdRs from the Pioneer. I just checked to see if it was still available and it is. J&R is selling it new for $129.99, half of what I paid about 11 months ago. I emailed by friend and he is going to pick one up just in case his W839 should stop working. He has been having some issues with it not wanting to finalize every 8th or so cdR.
I hope you luck out and can get it repaired for a reasonable price but if not, check out the TDK.
All the best,