[Station X]

That looks like a prefectly good analogue (moving coil) meter to me.

If you're using the X10K scale the reading needs to be multiplied by 10,000 or 10k.

50 X 10,000 is 500,000 or 500k which is correct.

Your results measuring the old pot indicate a crack in the track, so replace it.

A tip when measuring resistance, or indeed voltage, is to start with the meter on the highest range, in this case X10K, and progressively switch down the ranges to X1 stopping at a point where the scale is easiest to read.

If you have problems interpreting the reading on an analogue meter, you might like to consider purchasing an Auto-ranging digital meter. You just set it to read resistance and the result is displayed along with any suffix such a 'k' or 'M'.

Some people don't like auto ranging meters, but I'm quite fond of mine.