FWIW,

I used to own a 91 190E 2.6.

I bought it from my best friend in 97 when it had 75,000 on it. He flew a Cobra gunship in Vietnam and so was meticulous about maintaining equipment. Car always dealer serviced at exact intervals.

He told me that the transmission when cold would not shift right away. Needed a little warmup. Jump in it and head down the street cold, and it would lug along for 20-30 seconds before shifting with a bit of a lurch.
My 124 does not have this characteristic.
As the dealer said, the trans. was working properly.
It was annoying when you were in a hurry.

looks like what, 15 minutes, to install the tri-star?
That would translate to a shop rate of 90.00 per hr.
Not too bad.