Any time the output transistors fail, the TL071 has to be replaced with it. 

as for testing transistors, most of the sites do tell you to check it in ohms. Those sites suck and likely dont have much electronics experience whatsoever. 

The best way to do this is using diode check on your DMM. on an NPN, youll get .4XX to .6XX between base to emitter, and base to collector. positive on base. Reverse the leads, you get nothing. Also C to E you get nothing. 

PNP is the opposite. Black lead on Base, otherwise you get nothing.