u/Ok-Recording-8159

Looking for some advice from people who have dealt with this before.
I’ve got a ‘97 Chevy C1500 with the 5.7 and a 4L60E that I’ve been fixing up. It came with an aftermarket transmission cooler, but it’s still routed through the factory cooler in the radiator before going to the external cooler.
I was getting ready to replace the radiator anyway because it’s getting old, and when I started looking things over I noticed an oily pink film in the coolant. After disconnecting the transmission cooler lines, I’m pretty convinced the internal transmission cooler in the radiator has failed and ATF has been getting into the cooling system.
The transmission still shifts normally, so I’m hoping I caught it before it did any serious damage.
My plan right now is:
Flush the cooling system with the old radiator still installed to get as much of the contaminated coolant out as possible.
Replace the radiator.
Drain the transmission and refill it with cheap Dexron VI as sacrificial fluid.
Drive it just long enough to circulate everything, then drop the pan, replace the filter, and do a complete fluid exchange with fresh Dexron VI.
Check the pan for any signs that coolant made its way through the transmission.
Does that sound like the right approach, or is there something else I should be doing? Has anyone here saved a 4L60E after catching this early?
Also, once I replace the radiator, would you keep the transmission routed through both the radiator and the external cooler, or bypass the radiator and run only the external cooler?
Appreciate any advice.

Hey everyone,
I picked up a 2012 (I think) Exmark Pioneer S series with the Kawasaki FX691V and 52” deck from my uncle for $600. He thought the hydro drives were toast, but it just needed new seals and an oil change. It cuts fantastic now, so I’m really happy with the deal.
The issue is with the drive system. The spring on it (drive/idler spring?) isn’t stock – the guy who did the hydro work just threw a random one on there. I want to replace the drive belt too since the mower sat for about 3 years and I have no idea when the belt was last changed.
I ordered what PartsTree says is the correct spring, but when I install it where the old one was, it squeals like crazy and the mower barely moves.
Is this the wrong spring, or am I hooking it up in the wrong spot? The previous spring was much smaller (almost half the size). In the attached pics, I’m pointing to where the old spring was attached.
Any help would be greatly appreciated – diagrams, part numbers, or advice on where this spring actually goes would be awesome. Thanks in advance!