Patch 'gash' in shingles

I was just up on our roof and noticed a 2 inch jagged gash in one of our 3 tab shingles. The gash seems to go through both the top shingle and the one below it. We have not however noticed any leaking (yet).
The shingles are old and I don't have any spares and am not sure how/if I could match them anyway. So, I was wondering is there any reasonable way to patch the gash.
One possibility I was thinking about was to apply a couple of layers of tar paper to back of the shingle attaching either with epoxy or with the black gutter caulking. This would hopefully keep the sides of the gash aligned and fill in any gaps in between - I would probably also add a bead of the black gutter caulk to fill the gash from the front side too.
Any suggestions/comments?
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Carefully lift the tab and apply wet/dry roof cement UNDER the lifted tab. Press gently back into place.
I would use a builders shim and apply it about 1/4" thick and twice the width of the shim (or gash if it is bigger than I can see from here).
Colbyt
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Colbyt wrote:

You could slip in a piece of tarpaper coated on both sides with roof cement, which would seal bothe holes with a waterproof layer between.
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