Hi Mike,
I have used Permaplas for years and have several lines (Cortland 444) that are well over 15 years old that are still going strong.
Of more interest to yourself might be the Shakespeare Glider lines I have that were originally bought for Pike about 10 years ago. They have been "permaplas"ed a few times and still float high, are smooth, not cracked and are still supple.
As Ben says, for lines made by companies that sell line cleaning products, I tend to use them.