I have brown spot on my 8 -10 year old plant this year, Clematis wilt is due to a fungus that causes light brown spots on the leaves. It spreads down the stems and causes the plant to wilt. I removed all the affected parts of the plant and sprayed it with a fungicide, it has a lot of buds and I am just keeping my fingers crossed. I dont know if you have the same a pic would help?