Metal siding to cover masonite chimney surround?

I have a masonite chimney (steel flue pipe with a decorative wood framed "chimney" about 3' square, covered with some type of engineered wood like masonite). It has had a chronic leak problem. A couple of repairs by a reputable local roofing company lasted two or three years each. I want to get a longer term repair, and it can't wait until I get a new roof (within 5 years or so). The roof shingles are asphalt composite. The house is in Lubbock, Texas.
So, I had different local roofer come out to give me options and an estimate. One of the options would be to install flashing on the outside of the masonite, and then cover the masonite chimney with metal siding. This would supposedly reduce the maintenance problems associated with masonite chimneys (sealing/painting) which are often a source of leaks.
The other option was basically to rebuild, reflash and re-seal the masonite structure. As stated above, I would like to get away from the poor durability and maintenance requirements of the masonite chimney. However, I'm not sure what other options I may have.
Has anyone had experience with this type of repair? Would you recommend it? BTW, the roofer has given me several addresses of houses where they have done this type of repair, and I will be checking them this weekend for their cosmetic appearance. I'm more interested in how durable and reliable such repairs are, and whether there are better options.
Thanks, Randy
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