How did you determine the two JFETs Q1,2 were bad?
As I look at it, RV2 trims the voltage at TP1 to zero DC. Notice Q1, Q2 circuits are essentially the same, strung between +18 and -18vDC. Inevitably the parts will vary a little, so the trimmer is there to adjust one side so it balances the other. Adjust RV2 so you have zero DC on TP1.