Simple Ohms Law would be enough!
From a DC perspective R38 and R39 are in series and as both are 1K they should drop the same voltage.
210v - 180v = 30v dropped across R38,
180v - 145v = 35v dropped across R39
So one or both has changed value. It is very unlikely that capacitor leakage is involved.
If I remember, one of the modifications to this receiver was to connect an OA2 regulator across R40 to regulate the VFO and BFO supply voltages, you could do the same with a 150V Zener diode these days.
Brian.