Congratulations and welcome to the forum! You will love your Mercedes-Benz and can learn alot about it right here. There are DIY articles and links at the top of the page that will help you with the transmission adjustments. I bought a 1988 300E two months ago and am still working on mine (slowly). The main thing to look for first is any vaccum leak on the intake manifold and all the vaccum lines connected to it. Once you are not leaking there is a cable that adjusts shift timing. I put my sunroof issues off until last, because I opened it once and it took a 3 days to get it closed. As long as it isn't leaking, wait until you have the time and parts to do it right.
Which engine is in your car?
Chris

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1992 400E current
1988 300E sold
1973 280C totalled
1973 280SEL never got it running
1971 250C my first love but rusted out