The is a company in Florida that might be able to repair your existing DME/Immobilizer. The place is called Specialized ECU Repair. You can find them at
Specialized ECU Repair, Replacement, & Testing - Restore or Exchange your Electronic Control Unit (ECU).
Other forum members have had problems and had them do the job for a very reasonable price. I'd suggest giving the website a look and making a call to see if they can help.