You dont have to remove the liner, but it will give you a tiny bit more room to play with. You will have a job though as you have found it is really tight in there. There should be enough room to squirt in some soapy water with a squeezy bottle. My advice is that if they are not leaking - leave well alone, unless you have a new collet to hand. Because of how they are positioned the airline fittings on the back get cacked up and corrode. Mine fell apart when I came to change the springs last weekend, its worth noting that although the springs where knackered, the O rings where in tip top condition. If you are having sinking problems, its most likely that you springs are gone. Have a look at my post
here.