Thought it was leaky pan but now...

There are actually two seals in the linkage.
One around main linkage stem, and one inside it for the TP valve stem under the C clip and washer.

The one in the case is kind of a PIA unless you have a slide hammer you can put a washer on to pull it down in the case from the top, or there are a couple of other creative ways of doing it.

Note that you can get a taller seal for the case in case the shaft on your valve body is grooved.