The last two instructions in the manual on page 20 provide the directions for which pot to install in each hole. One pot will say "B100K" on it and one will say "A10K". The black writing you showed in your photo is not where those labels are, and I bet that same black stamp is present on both parts (it will face in opposite directions).
You need to at least pull the nuts off one of the pots and slide it out of the chassis plate to examine the surface that faces the chassis plate to determine whether it's the correct part, or you could set your meter to DC resistance and measure between the outer pairs of lugs on the upper and lower levels of the pot that's in the hole for the volume pot. If you get about 100K, you have the pots swapped.