A shorted out heating element is certainly one possibility. You would have to risk the cost and time to get a new element and install it, if they are still in stock, or use the funds and imputed labor cost to buy a more modern replacement unit.

As a simple test, attempt to use it and when it trips the breaker, immediately unplug it at the wall receptacle and feel over the cord length for hot spots. If none then a cord short can be eliminated.

Modern AFCI breakers can also trip if there is an arc due to some part of the circuit opening up rather than shorting out. This should also be considered. It may occur in the heating coil.