After using a P1 back since 2008, wet cleaning is just part of the use pattern, as a P1 back needs cleaning pretty much after every use, (at least on a tech camera, and most times on the XF).
I would consider using the Visible Dust swabs, I believe now P1 is using them as with the IQ4, they included a set of them or something very close to the same thing. Note the V Dust swabs are not the full size of a IQ 3100 or IQ4 sensor, but instead are designed for the cropped MF sensors. You should also still be able to find the old P1 plastic card that came with their cleaning kit which you wrap a cleaning cloth around manually.
The cleaning kit from P1 has 2 solutions, A is a blue color and is meant for very serious stains, I guess finger smudges or oil. I have never had to use it but one time on a P45+. The clean solution B is what you will use most of the time. Make sure to only use a couple of drops of fluid on the swab, as that's all it takes. Then wipe in one direction, and flip the swab and cover the other side. Should never reuse a swab, it's wasteful, and one reason I use the older P1 plastic piece and square cleaning cloths, much cheaper when you are cleaning all the time.
NOTE, you are note touching the actual sensor, you are touching the cover glass over the sensor. You will never touch the actual sensor. You can scratch that cover glass, but it's pretty tough material. I have never scratched one.
You can use the Eclipse fluid, or Phase Fluid or the Fluids sold by V dust, all work the same.
If you have stubborn spots, and have attempted to blow them off with a blower, and they are still there, it's time to wet clean.
Also, I would recommend doing this yourself, and just getting use to the process. The GFX series of cameras have no mirror box, thus you can use either tool I have referenced since you don't have to drop down deep. One nice thing on the P1 back, is that it's by far the easiest to clean, since you can remove it from the camera have total access. Here is a link the the cleaning set sold by Capture Integration, just an example. But they have all you need to get started.
https://www.digitalback.com/product/ci-sensor-cleaning-kit-2/
Paul C