Have you been able to establish where the leak is coming from. (Overpressure and use soapy water witha paintbrush) If it's valves then that is fairly straightforward, it is best to coat all the seams that you can see to look for bubbles as well as any sections which are scratched or scuffed.
The Seams on the searider are at the bottom of the tube and not behind the rubbing strake and as such run along the fibreglass flange section of the hull which makes detecting seam leeks very hard.
The upside to this is that you can use a Sealer available from Polymarine:
This will work well as long as you have the means to tilt the boat backwards and forwards which will cover the seam internally at the bottom of the tube.
With regards to the transom it would be worth tapping it with a hammer and listening for a dull thud which could indicate soft wood behind the Fibre glass, it will also flex.
I hope this helps.