727 Transmission Speedometer Sending Unit

I did a search in the MoparForum archives and didn't find any posts relating to this topic, so either I did an absolutely lousy job at searching or I'm the first knucklehead with this issue.

I noticed my interior speedometer gauge which is original to the car not working last trip out and then after pulling into the garage I took a look underneath the car. I noticed a small leak that appeared to be coming from the speedometer sending unit that does into the transmission.

I'm not sure if the unit is broken or just leaking and needs to be tightened and therefore not functioning. I believe the sending unit is original to the car, so perhaps I could just purchase a new sending unit and install it. If I went the latter route, where can I purchase a sending unit for a '69 727 and would that require removing the dash? And or what steps might be involved? Would other material purchases be required (domino effect) if I replace the speedometer sending unit?

Thanks in advance.
Author: inri