Reparing "Live Bait Well" Cement walls

I have a 1927 cottage with loads of project opportunities, one being repairing an old outside, in-ground bait well.
Roughly the well is 36" x 14" x 14" deep. Water gently flows in one side and out the other.... It has 2 x 4 frame wood top and 1each 2 x 8 wood on each of the 4 sides with approx. 2" to 3" concrete walls and bottom.

My problem is the concrete, especially on one vertical length is crumbling and has grass coming out of the top surface.
I can remove the water and I think can stop the incoming water for a "while" if needed. Even so the water only trickles, so would take a couple days to fill back up. (Also the well has water in it most of the year and the location is Ohio.)

Now the question is what would be the best concrete or other material to fix the problem. I already have some plywood cut for forms so I could fill between it and the concrete surface. I was going to drill some holes in the deteriorating surface and place some nails or something so the new concrete would secure onto the old??
Lastly I don't know if it then needs any sealer as this has lasted maybe 60+ years with none....

Any recommendations would sure be appreciated.....