I have a wood stove with a 7" collar that I want to install into a fireplace. The chimney is a 7X11 clay flue. I need to install a 6" liner. I have an old (true 6") liner but I wonder - do I need to buy a new liner (actual 5.5")? The two issues I see are 1) getting a SS liner down the chimney with mortar clumps in the way, and 2) How do I get a SS flexible liner past the curve in the flue that passes the damper from the main floor without damaging it? Due to cost, I would like to use my old liner aqnd especially do not want to call in a chimney expert to pay thousands of dollars. Any suggestions or hints are appreciated. Thx.