squeal sounds like it's coming from the inside of the unit, not the reel itself, and only during playback.
There are no belts in the Fostex G machines.
The motors and rollers are all moving during FF/RW...so the only other mechanical piece that would move specific to Playback is the Pinch Roller.
Can you get your ear close to the deck during Play, and see if you can pinpoint where it's coming from.
It could be tape squeal, but it could also be the shaft that the Pinch Roller sits on.
From the pictures....the deck looks pretty clean, so start with a complete deoxit/cleaning...and then see where you are.
Careful around the idler and tach rollers...and all the rollers for that matter when you remove them....there are very thin washers that you may not notice until they end up on the floor. They will stick to the ends and are hard to see.
Also, there are bearings inside the rollers, so just go step by step, and put everything back in reverse order.
Don't oil/lube up the rollers too much....maybe just use a Q-tip and put a light film of silicone on the metal parts that move internally (don't get it on the outside)...and watch out the the left roller (the one with the rubber)...there are small senors in there and a strobe disk attached to the back of the roller. Don't let the silicone touch it, as it can easily remove the printed strobe pattern, and then you'll be fucked.
If you plan on getting into the front of the deck...you have to remove a lot of the Allen screws but first the cover piece that goes over the transport. Take off the head cover....then all the rollers....then the cover plate...then the bigger cover plate that goes up over the reel motors.
Keep close attention to what you are taking off so you can put it back in reverse.
The cards will come out below, so you can first deal with the mechanical overhaul...then go down to the cards. With them, I would just pop them out and clean the contacts with some DeOxit, then pop them back in.
You probably don't need to pull any of the main system boards which are accessed from the back. Just clean all your connections in they back.
When I first got it back in the early 90s I had it sync'd to Cubase on an Atari ST...
You're taking a page out of my life.
I ran my G-16C which I got in 1990, together with my Atari ST and Steinberg's original Cubase sequencer.
Had them locked, with Cubase having full control of the G-16 thanks to the proprietary drivers they had written just for the G-16.
I actually did a whole article that was published in the Cubase newsletter, describing the process and how to do it...I think I was probably the first guy to marry the G-16 with the Atari and Cubase.
I still have the Atari...which I was in service until maybe a few years ago, where I changed my studio SOP around, so I wasn't really needing a separate sequencer, since I had moved over to a full-tilt DAW several years earleir...but I was still firing up the Atari when I wanted to just do a quick sequence, as I found it much easier on the Atari than doing MIDI in my DAW.
Now I just use the MIDI sequencer in my DAW, but I still miss those Atari/Cubase days...I could work so fast with that setup. I also had 32 channels of MIDI Mute/Volume automation using that rig along with 4 Niche modules (also gotten from Steinberg)...and I had them hooked up to my TASCAM 3500. I stopped using the Niche automation about the same time I started using the full-tilt DAW, as I could get all my levels done in the DAW, then just mix out through my TASCAM console (which I still have/use to this day).
If you run into any obstacle with the overhaul...post up your problems, I might be able to help, since I've had my G-16 apart a couple of times for cleaning and stuff.
Do you have the schematics with exploded view diagrams? They can be helpful when your are disassembling and reassembling.
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