If you have just replaced they are usually all good. I agree not to use P/Mate. Does sound like there maybe a fault or crack in the pan. Or a small drip from the cistern feed? Water does travel...
Looks to me that it is Clay Pipe coming up out of the ground and a S-Type pan connected to it. What pan have you purchased? If it is a normal HO (Horizontal outlet) they just get a Swan Pan connector or a flexible one but they seem to store dust and dirt on the concertina.