yeah 14.000.00 showing and actually being 13.000.95. it's not a lot, but it is annoying. with that fan sucking the heat out it stays right on freq. with summer coming and it being used for fsk it should be closer than that.
The answer to the non-problem is contained in the above quote; "it being used for fsk". FSK is a 100% duty cycle mode and generates a lot of heat. The stock 570 uses a reference xtal that is not insulated from chassis temperature changes(final and PLL mounted to same aluminum chassis) and will change as the temperature changes. The 50Hz drift is well within the spec of the stock radio. Per owners manual less than +/-10PPM from -10 to 50 deg C. That's +/- 140 Hz on 20M. Since the "normal" Kenwood temperature circuit turns on the fan at 40deg C (105 F) I would guess the xtal would move. Actually that's a small amount of drift under those circumstances.
If greater stability is desired/required then you can Band-aid (FAN) or fix (TCXO), your choice. Realize the fan fix will only work up to a certain temperature (summers coming). I wouldn't change the internal fan circuit.
Since the SO-2 TCXO option is hard to find go to Product Reviews and search for "N3BA VCTCXO Module" It may solve the problem.