WyoBolter...Tim's covered all the bases on this one.
Cutting the old rubber is by far the safest way to preserve your glass.
Just dont slip with the knife!

Here's a link to
Steeles They're not the cheapest but the genereal consensus is,they are the best.
It won't hurt to replace the rear rubber too,if it's the original one.
Especially if you're going this far.