Kate .. the seller will "probably" say you drove it, it's your problem ... "Caveat emptor" ... which is of little help...
IF the bulbs have been deliberately removed to hide the fault, you "might" have a case under the sale of goods act, best advice would be to talk to your local Trading Standards Office, or you could say the sale was fraudulent ... however, proving this could be very difficult.. all the seller has to say is "it was like that all the time I had it" or words to that effect .....
SO, lets talk about fixing it ... replacing the bulbs is a 30 minute job, easy to do and there's a guide
http://www.omegaowners.com/forum/index.php?topic=90618.0If that results in the TC and ABS lights being on with no speedo its the ABS ECU that's failed .. a known problem.
You have 2 options .. get yours fixed .. about £130, or get a 2nd hand one, be cheaper BUT it "might" be about to suffer exactly the same fault .. you just don't know. The actual job is pretty simple, but very frustrating, as you are working blind on the screws that hold the ECU to the pump body. I got mine off OK, but the last 2 screws took some getting in .. and lots of cash in the swear box !!
http://www.omegaowners.com/forum/index.php?topic=90627.0HTH