OP, Relief from what - the water is already under the felt & into the roof,anything you spread on the felt will only seal in the continuing water damage.
Gas from the previous leaks is already pushing up here and there, and will continue to swell with bubbles & ripples opening up the attempts to even temporary waterproof esp. around the damaged corner of the light.
Nothing for you to lose by having a go - but given that summer will give you an opening for roof work its worth thinking about a new roof.
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