Transmission Issues - Valve Body?

So I had my 98's transmission checked out the other day just because it's been hesitating when the pedal is NOT floored and, at times (rarely), shifting hard; here is the technician's diagnosis. He explained it to me over the phone but I'm no transmission expert so I didn't totally follow him. But, this is the written diagnosis word for word:

"Vehicle will lose torque converter lockup despite the lockup solenoid applying a 100% duty cycle. These units have a common valve body failure that will result in loss of fluid pressure and subsequent damage to the torque converter and internal clutches. The following service is recommended: Internal service ($500)."

I know that my family's old 2000 Buick Century had a transmission valve body problem that basically destroyed the transmission... it couldn't shift without bucking. That led us to sell the car because fixing the transmission just wasn't worth it for (imo) such an... how do I put it nicely... uninspiring vehicle?  

Does this sound like a "common" issue like the technician claims? I'm on the fence about getting service done but he recommends replacing the transmission eventually. Any help will be much appreciated. Thx!  

The most common issue with any 4t65e HD is the Torque Converter Solenoid (TCS). It will cause slipping, and also bang shifts. The scanner will read 100% Duty cycle,  because electrically the Solenoid is ok (otherwise you'd have a code). What happens is that it gets gummed up internally, and intermittently doesn't work properly. It's literally connected to the Valve Body, but doesn't require VB removal.
It's possible there's some debris in the VB itself, but unlikely. A trans flush, in this case, might just fix your problem. No guarantee, but it's worth a shot.

I did a Write-up for replacing that solenoid when mine started failing years ago. It's in the Write-up section if you want to have a look.