500sl clunky shifting

[BIGBIRD]

i got a 1990 500sl for free (it wasn't cared for at all) and on the ride home, i noticed that every time the car would shift, it would do so very roughly and from what i can remember, kind of loud too. ps. the car has 138K miles and i have no clue what the service history was like. ie. fluid changes or tune ups, but i can tell by the condition of the rest of the car that the weren't peformed regularly.