Metal Roof, Leaking at the lap joint screws

My detached garage has a roof section that is a VERY low-pitch metal roof. Low, as in probably less than a 6' rise in 45 feet. The metal panels are installed over tar-paper over plywood.
The metal panels are long enough that there are only 2 required for the run down the pitch.
I'm getting consistent leaking across the roof at the 1st plywood joint that's below the panel joint, most of the roofing screws at the joint have their washer deteriorated and hardened, and some have been leaking long enough that they are loose from the plywood rotting.
The amount of plywood that is rotted is limited to a small strip running across the pitch, and only around the screws, and I am not going to strip the roof to replace it.
My plan is to get new screws, and replace the screws where the wood will hold the screw. Where the wood won't hold a screw, I plan on going a little up & down the pitch (a few inches) and putting in a screw.
My question is, for the spots where the wood won't hold a screw, should I put a bunch of roofing spooge on a new screw and shove it in the hole, or should I fill the hole with silocone or roofing spooge?
Also, what is the likelyhood that water is migrating backwards up the lap joint? If its likely, should I raise the top panel slightly and apply roofing spooge between the panels, or should I just apply some spooge over the top of the joint? Ditto ques. for sealing tape (which I hope was used in the 1st place...)
On the day I was on the roof, it went from sunny and 55 degrees to cloudy, rainy, and about 45 deg., and I could see the panel joint move by about 1/4 inch.
-Dave
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With such a low pitch, and especially if you're in snow country, I'd assume that the water is wicking back up between the panels.
If you're not going to pull the panels, you're going to need to seal _everything_ you can (with at least a 2 inch band under the overlap), and probably goop the new fasteners you install. I think roofing goop is the stuff to use, the silicone will fail. You have to get the upper panel lower edge solidly anchored/sealed to the lower panel with something that has some give.
Likely part of your problem is the upper panel "working" against the lower, and wrecking the seals on the screws.
--
Chris Lewis, Una confibula non set est
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What opinions can I get about slipping membrane or felt into the lap, under the upper panel and over the lower panel?
How about sealing old screw holes with aluminum foil tape? Scary putting Al aganst Fe, but if I go for a temp fix for the winter, it'd be removed in the spring.
Dave
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If the material is the slightest bit porous, it'll make your leaking problem worse rather than better. I think it's best to use the proper roofing sealer goop. Especially if you're lucky and the sealer can be applied above a purlin to minimize joint movement.

The proper roofing goop wouldn't have the time limit. Foil tape probably last longer than a year anyway.
--
Chris Lewis, Una confibula non set est
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use an elastomeric paint like: http://www.koolseal.com/steps_elastomeric.asp http://www.henry.com/Cool_Roof_Coatings.28.0.html
If done properly, you won't need to replace your roof and the leaks will be taken care of.
(top posted for your convenience) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net

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