I have never seen the coverplates used like a coverslip.  The system is
designed to hold a slide in such a way as to allow reagents, etc to added
at the top for immunostaining, basically a gravity displacement/capillary
gap system, then the coverplate is REMOVED at the end, the slide is
coverslipped with an appropriate mounting media.  

Coverplates here are reused.  I usually remove the coverplate BEFORE
chromogen step, in order to control color development, and that keeps
chromogens from staining the polycarbonate plastic for another use. Care is
taken NOT to scratch the coverplates, if so, they are tossed.  
Gayle Callis
MT,HT,HTL(ASCP)
Histopathology Supervisor
Veterinary Molecular Biology - Marsh Lab
Montana State University - Bozeman
19th and Lincoln St
Bozeman MT 59717-3610

406 994-6367
406 994-4303 (FAX)