TS-180S operators may report intermittent DFC instability, especially at 10 KHz even points. This may be characterized in some cases as PM'ing.
On the VCO unit X50-1550-00, install a 330 Kohm resistor between Q11 G1, and the 8V line. Connect from L7 at C12 to Q11 G1. at R35.
No adjustments are necessary.
Note: On page 37 of the Service Manual, the Board view of the VCO unit contains reversed callouts for Q11 & Q15 FET's, D & S, and G1 & G2 are transposed.