Oil leak from ALDA

[Yuros]

I removed the ALDA unit on my '87 300TD a few weeks ago as it was not working properly and caused lethargic acceleration. Removing the ALDA made all the difference and I noticed drastic improvement in performance and smoother shifting.

However, I have now developed an oil leak from the opening where the ALDA unit was mounted.

The instructions for ALDA removal on this and other forums are quite straight forward; Remove ALDA, drive.
Should I have capped the hole, or is it self-sealed? Is oil coming out of that opening normal, or indication of some other problem?

My mechanic tells me that if ALDA is working properly the car would actually accelerate better than with ALDA removed and recommends that I repair the ALDA and install it back. However the improvement in performance and shifting was so significant that I'm very reluctant to put the ALDA back on. But I can't have the oil leaking from that hole either....