Flashing a chimney without re-roofing -- suggestions?

Hi guys -

We had our 10 year rain last weekend in Massachusetts, and my wife noticed some water coming into the 2nd story bedroom ceiling. I went up to the attic and saw the leak coming in around the (gas boiler's) chimney. Looks like when the previous owners re-roofed the house in 2006, they didn't bother reflashing the chimney.

Has anyone redone the flashing without doing a whole roof job? The shingles are in good shape. The roof is at 12/12 pitch, and the leak appears to have been on the "uphill" side of the chimney. Any suggestions appreciated.

Loosen (not remove) all the shingles round the chimney, buy some lead. use a grinder w/ a diamond wheel to remove the lead tucked into the mortar joints. clear it all out. Then, and this IS important, individually form every pice of lead, especially the long strips in the back. Put a pice on, form it by molding, bending, tapping with straight edges and a hammer. Once you have one piece done, set it aside, and fit another to where it has to go. Once all the lead is pre formed, THEN start weaving it into the shingles, and repointe the joints where the lead tucks in as you go. Don't get 100% picky about it all being exactly crinkle free at this point. Let it set for 24 hrs, ideally, and then tap out the crinkles and seal the seams w/ some pro-flex. tap the loose shingles back down after its all set up.