For what it counts and based on your initial message you may not need to replace the polycarbonate just the rubber seals and maybe underside spacer strips if any.
Plastic conservatory roof leaking.
Leak below roof vent due to failed poor mutin bar seal above or below.
Leak through the roof vent.
The fowong butyl tape works to repair cracked roofs across multiple surfaces including metal fibreglass wood textile plastic aluminium and more.
A conservatory roof leaking in centre could be due to a slipped or incorrectly fitted roof panel a cracked glazing unit or a perished seal.
Our advice would be to get a conservatory roof specialist to visit and check out the scope of the repair work.