As long as the Fluid level is kept with in normal limits the leak will cause no issues.

"It had leaked at about a rate of 1/2 quart over the last 5k miles." That does not seem like a big leak to Me.

It the Leak is at the Seal on the Front Shart the Transmission has to come out just to change the Seal.
If there is a Groove worn in the Shaft some People install a "Speedy Seal" set that include a tube that slides over the Shaft and covers over the Groove so there is a smooth area for the New Seal. But, that set is aproximately $45.

I have a leak in that same place. In the first Year after buying My Mercedes I finally found this Forum. What I read was to use Lucan Transmission Sealer Conditiioner.
That reduced the leak to a tolerable level and also improved My 3-4 Shift that had been flaring badly.

I have kept using the Lucas stuff since I have owned the Car which I think is 6 years now.
The Lucas stuff reminded me of STP but pink. And, that might be how it works; making the Transmission Fluid thicker would decrease leakage and increase pumped Fluid pressures.

Other Members do not recommend any sort of addatives period. So, what to do is up to You.

My Driveway is Old, I put Cat Litter on the Drive Way and spary something like a Driveway Cleaner or Purple Power on it once in a while to clean any Oil Stains.
All of My Vehicles leak something go some extent.
I have also at time used one of those Sheet Metal Drip Pans under the Car.

If you don't want your Driveway stained you will have to make a choice in the expense of resealing over the looks of your Driveway.

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84 300D, 82 Volvo 244Gl Diesel