There is no public, free "VIN decoder" style website for Allison serial numbers. Here is the correct workflow:
For mechanics and fleet owners, DOC is the gold standard. Allison Transmission Serial Number Lookup
A: Only if the previous shop uploaded the repair to Allison’s Global Service Database (GSD). Most independent shops do not. Dealers are required to upload warranty work. There is no public, free "VIN decoder" style
If you bought a used Allison without a confirmed history, run the serial number through (available via a distributor). Why? Because stolen heavy-duty transmissions are a real problem, and Allison will flag a serial number that was reported missing. There is no public