Our shower is leaking through the ceiling in the shape of the shower cube. I can only presume it's the sealant but it locks a strong seal around most of it. Is it just a case of re- sealing?

Be more concerned with the drain line. The water must flow only into the drain tube & not around it. Consider a possible leak in the drain plumbing.

Best bet would be to open the ceiling up and see what's what the sheet rock that has been wet needs to come out anyway. Also is the ceiling leaking all the time or just when the shower is in use. Post back and let us know.
Good Luck, AC

I agree with AC. Open up the ceiling and check wher the moisture is. Is it around the trap and raiser or more from the side. Could be a ruptured drain seal or tile grout that has shrunk. But you'll ne4ver know until you check. Good luck, Tom