Mr Heat,
Depends on how much time you have and how much patience. There are great kits availible from Ecklers or Mid America. You can buy the piece that you want or a whole kit. Beware, they are replica kits and are a bit thicker but will do just fine. Takes a bit of time and a steady hand but can be done. Just be patient though and don't rush through it. I had all of mine replaced. Bought the car from Arizona and the all of the seals were cracked and split badly. Had some serious leaks not only from the top but the windows too. After replacing, no probs at all. Plus, I live in Western WA, rains every other day. Good test for the seals for me. Regardless, call around if you are going to let a mechanic do it. Can be pricey because of the labor.