So multiple print drivers produce the same result? Shouldnt be a driver issue then.
A few options remain:
1. A configuration issue with the application
2. Firmware update on the printer
3. A font issue on the PC
For configuration issues with MS Office products you might want to stop by the MS forums and see if they have any suggestions.
To confirm a printer problem it would be best to try installing and printing on a similar OJP 8100. Considering you mentioned this is a special case that may not be possible. Firmware updates are simple enough if one is available for you.
Font issues happen when a user attempts to print in something custom that the printer does not understand. Normally swapping the print drivers will give you some kind of progress in this area, but then again there are some really wierd fonts out there. It might be helpful to try reloading this customer with a fresh Win7 install and only Office. Once you have the enviornment cleaned then test printing again before attempting to run any file backup and recovery software. See if the defect is present from a clean slate or if the user is doing something funky to fool the printer.