Just buy a new timing belt tensioner bracket. the tensioner and pulley bolt to a bracket, not the engine. so you can just replace the bracket itself. get a used one or a new one for $35 from subaru. it's held in place with like 3 12mm bolts, remove them and the bracket comes right off.
you can also repair the threads with time serts or helicoils. M10x1.25 threads.