I know, but if you already have a pit that's got a slump pump in it, you can use that.
It's leaking from the centre spindle. Hence it's going to be the gland washer and perhaps also the head gear washer that's crumbled. Either way it needs to be opened or swapped out.
Then can you not put some easing oil on the threads for 24h and afterwards back off and re-tighten the gland nut without taking anything apart at all?