put your head down and turn it so the "good eye" is lower than the hurt eye. blink a gazillion times and the particle will most likely go toward your nose and then you can take a match torn from a matchbook and, using the soft torn end, gently swab the particle from your eye.
i have also had...
"particularly from one corner"
down low near the roof rafter wall intersection? are your gutters backing up in a downpour? is there a heat source and or southern exposure so the dark stain may be from ice dams last winter(s).
try going into the garage during a heavy rain. take a flashlight...
does the vise open or close long distances by turning the handle 1/2 or 1 turns and then just pulling/ pushing the jaw? could be the play in the worm is designed to enable this feature.
what would be the advantage?
part 2: (based on below response) why not just adjust the glycol mix? meaning 80% greater heat transmission for the identical amount of degree protection?
further 'google' did prove additional DuPont Tyvek products available for roof application. most of them involve application to rafters in an unsheathed (i.e., no plywood) or 'skip sheathed' roof such as slate & tile. the big selling point seems to enable moisture disapation at the underside of...
http://www2.dupont.com/Tyvek_Construction/en_US/uses_apps/homeowners/FAQ_homeowners.html
there's a good reason: it isn't marketed for roof installations.
use ice & water shield to keep out, well, "ice & water". most of the roofing companies have got on the wagon and brand their own product.