The logic is this: transmissions have been known to fail immediately after a flush...so avoid a flush to avoid the failure. The theory is that a flush will dislodge some old gunk that causes the failure.
Personally, I don't buy the logic. If the trans is close to failure, then flush vs. drain and refill won't make much difference. You're using the transmission pump to do the Gibbons flush - and that's exactly the same flow/pressure that happens when the transmission is running...so it's not going to dislodge more gunk than it would when operating...The Gibbons flush will ensure that all the fluid is replaced. Drain and refill replaces about half. Do that 3 times and you're at 7/8 new fluid...
In your case, the valve body was done - and the trans should have been flushed as part of that. So, feel free to flush it every 30K or so to keep it working correctly. Just make sure that you use a fluid that meets JWS-3309 spec, those fluids include Toyota T-IV and Mobil 3309 (among many others...) as well as the Volvo fluid. The only advantage of the Volvo fluid is the cool little container and the pleasure of paying 4 to 5 times the price for the same stuff...
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