I purchased two x 50ml tubes about £5 a tube. Or a bit less.
When I last did the job I just renewed the two seals. I filled them both to the brim almost and fitted the into the metal unit. Leave the Allan key bolt out for now as any excess will come up through Allen key hole.
You must make sure the new seals are sitting as tight as possible in unit so give unit a good wipe out.
Overfilling can start to push seals out so take care as you inject grease. Best thing I found two put grease in is a medicine syringe from a chemist, cheap so buy two in case you break one. Squeeze grease tube into end of syringe after pulling plunger out which is Chinese plastic and snap easy hence I urge you to buy two
I always when adding grease after an engine service or if engine hours are less than normal perhaps yearly or longer whatever the time frame, spin the shaft as you gently squeeze in the grease watching the seal you can see stays in place.
If seal moves stop adding grease of course, leave Allen key bolt out, squeeze seal evenly back in and excess grease will exit Allen key bolt. Replace Allen bolt.
Of course if just topping up already fitted unit one tube is plenty but why not get two tubes and spare seals and your ready for anything without worrying where to get the parts quickly.