Wow, MY KIND OF CAR!
I would love to have a manual transmission five cylinder 123 car, especially a five speed, protect it and cherish it.
I'm surprised that you can't get a Y from Performance, I would suggesting posting this question to the Parts Shop here. I expect that they will find one for you.
Wow, a five speed, turbo, 300D, I've even considered trying to build such a car.
'01 C Class, Six Speed
'84 Euro 240D, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in