Well - i fixed this on my old 19TZD over the weekend.. lots of work doing this job!
The seal on this pump had a kind of steel sleeve around it - I tried unsuccessfully to remove it on the car but lack of space and how stuck it was stopped me.
Once the pump was off the car and in a vice it finally came out with a long, thin and sharp screwdriver - the rubber seal was mush, I'm surprised it lasted as long as it did!
I changed a few more of the easy seals on the pump but nothing else was leaking. I should have probably done the pump head seal too as this is not easy or likely to go very wrong if attempted on the car but time was against me and I needed the car on Monday.
Changed the cam and crank seals, new belt on and back together it started perfectly and doesn't leak!
I hate to think of the labour cost in a garage for this job - most local diesel specialists quote around £375 for a full reseal and testing the of the pump without removal and refitting..It's these kinds of jobs that can scrap an older BX like this given it's low value - I'm just glad I persevered and did it myself.