Hello Ray. You might want to post this in the Corvette Tech and DIY section. It will likely get more viewers. Might also let them know who you've been using for a caliper supplier and the brand name. Here's the link.
canadiancorvetteforums.com
The lip seal ones drops down from the weight of the piston while sitting over a period of time and start to leak. But having said that, I have filled the reservoir, drive it and the seal would rebound and work over the summer, but after each winter the problem would surface again the following Spring. Got so fed up and converted to an o-ring style piston, and problem was gone for good, at least that was my experience. Got mine from Vette Springs & Suspension years ago. Came with stainless sleeves as well.
