vacuum modulator disconnected?

[HeavyDuty]

Greetings all, newbie here. Great community of MB owners here, hope to be a long time member.

Got a problem I hope someone here can help me with. I recently purchased my first MB, a 1990 420 SEL. Absolutely love this car. First thing I did when I got her, as I usually do with a newly purchased auto, is changed the oil and looked her over really good. While under the car I found a vacuum line disconnected from what I think is the vacuum modulator (round, about 2 inches in diameter on the side of the tranny with one vacuum line attachment). Needless to say I connected the line and now I am having shift trouble. The tranny seems to be hunting gears, particularly between 3rd and 4th. It seemed to soften my shifts a little, more like a luxury car feel, but now it hunts between 3rd and 4th and sometimes between 2nd and 3rd. It seems to have a mind of it's own. I do not know how long it has been disconnected and when I reconnected it the car went back to normal (good shifts at right time albeit a little stiffer). Question is if this modulator (?) is diconnected can it damage the tranny? It runs and drives great without it. If there is a repair involved is it likely to be a costly one and can I drive the car without it being connected until I can get the repair done. I don't want to end up on the side of the road with the wife and kids if you know what I mean, but after just purchasing the car I can't afford a major repair bill either.

Forgive me if this is a little lengthy, I am not exactly Mr. Goodwrench however I want to make sure I give everybody enough info to help me out with this. Thanks for reading, any help is much appreciated. HD