Change ATF in torque convertor ?

[john493]

C350 estate petrol 2012 with the V6 M276 engine & 7G-tronic transmission - yes it's a rare car in the UK.

I'm going to change the ATF. I believe the torque converter (TC) will have a drain plug, but do I really need to change the ATF in the TC ?
My understanding is that although the TC primes with fluid from the transmission pan, once full that fluid just stays in the TC & is effectively separate from the ATF in the transmission.

Any views ?

[Stegel]

I have changed ATF in around half a dozen 722.6 and 722.9 gearboxes, and have drained the torque converter each time; only a few litres comes out of the TC, but in each case it was as dark as the fluid drained from the transmission sump, so I think it’s important to prevent the new fluid being contaminated with old and dirty fluid. After the fiasco of “sealed for life” transmissions, Mercedes include draining the TC in their workshop procedure for ATF and filter changes.

[john493]

Thanks - I think I'll drain the TC too then.