Common issue with reverse going out. Don't waste your time and money with filter change, its done. Best case (unlikely though) you'll give yourself a few more weeks then it'll give out completely.
You can live with it right now since usually other than reverse everything will work fine. But obviously you'll have to park accordingly and it can be somewhat dangerous in case you need to reverse in traffic.

I recommend Sun Valley Dismantlers in CA, they can ship you a rebuilt 722.3 for $1650 incl shipping. They are pros at MB transmissions.

I'm at 2k on my rebuilt from them and its running like a dream.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k