I have a big agnes insulate air core sleeping pad that's been handed down to me from my brother. It has served me well for over 3 years but by the end of this summer developed a slow leak. Generally by the end of the night I'm sleeping on the ground. I have not been able to find the leak. I've tried submerging the mattress in my bath tub and look for bubbles. I've also tried the soapy water technique that basically involves applying a slight layer of soap water and looking for bubbles to form from the leak.
I would like to fix my current mattress, I can't really afford a new one right now. Does anyone know some other techniques for finding air leaks?