Straight 6 (211/later w220) is the better of the two as is the 5 speed gearbox attached to it, sbc would let it down though in the 211.
V6 (642) has a few common issues that are not cheap to fix and comes with the 7g tronic gearbox.
It will be the pipes, a short 90 degree one and the other with a plastic housing around it that goes to the pump.
Make sure that it is a diesel leak underneath and not oil, oil cooler seals are quite common and not a cheap fix.
Just undo the rear unions on the suspension bags to let the air out, the car will automatically re-fill on start up.
To bleed sbc you will need either a decent diagnostic machine that activates the sbc pump or a good quality brake pressure bleeder.
You have driven the car relying on the oil that was in the torque converter, as I said add 4.5 litres of oil, if it still won't change you may have to get the codes erased from the gearbox control unit, alternatively sell me the car for 5k and I will do it
I'm assuming all this has been done at home and now the car doesn't drive?
Start again, drain engine, change filter add engine oil.
Add 4.5litres to the transmission tube (the correct one this time )
If there is not enough oil in the transmission then it can't create pressure to work, is this...
Has your sport even got sbc? I'd imagine it has abr, this means stadard bleeding method will work and changing the brakes won't come with any warnings!
Do check though!
As for bleeding sbc with the pedal it will never work.
I have Bose in my c43, when I bought it the car it was running a Sony head unit, I wanted to run my alpine so perchased a similar unit to the above, it made diddley squat difference!
I'm aware that the Bose amp and speakers run at a lower ohm rating but seriously there was no audible difference.