Hey mikeskory, as Samuraipanda suggests, it's also a good time to change the input jack socket (it takes the most ware over the years), it's an easy swap out/in in the MP-2 but you need to use a switching jack socket with a slightly longer thread to normal (@MJMP what's the switchcraft part number ?). I got a few jacks from MJMP when I bought some other bits from him.
R913 is under one of the tubes so you have to take the tube out to see/get at it. See attached picture in the noise mod instructions which also shows the test point just above it (the pic shows the new R913 resistor (blue) not the original (beige). Measure at the test point first (dc volts, +ve on test point, -ve on case) with unit on, tubes in etc but lid removed (careful !!). If you get around 187Vdc (up to ~190Vdc) then this is probably not the problem and it's more likely to be the jack or tubes. IIRC, above 190Vdc is where the problem starts as the resistor fades over time ?? All 4 of my MP-2s are a little less than 190Vdc (with or without the new R913 (2 have new R913, 2 don't and are still fine)). If you search my MP-2 posts I listed the various test point values in my MP-2s.
If your tubes aren't reasonably new, I'd change them (and the jack) out first (I "highly" recommend a pair of New Sensor Mullard 12AX7 re-issues long plates, perfect match in the MP-2).
To change R913, don't do it from the top (like one youtube video does
). You need to take off the bottom cover (easy) and desolder/solder from underneath. Be careful not to overheat the pads (I did and wrecked one of them
). Let us know how you go (maybe start a new thread ??)