Have asked on here before and got sensible answers, so here goes.
Got a bit of a leak on the roof, due to old mortar flashings having shrunk away from the chimney. We’ve got some scaffolding going up tomorrow, and my initial thought was just to patch up with more lime mortar and sort it out properly when we replace the roof.

F-I-L suggests doing a semi-proper job with roofing lead. Cut a chase into the chimney stones and bash some lead into place. I have two problems with this though:

1) he’s suggesting just using a single sheet of lead, rather than 2 layers, and cut the chase diagonal following the line of the coping stones – this seems to be just asking for the lead to slide out of place, and for me to make a huge cock-up of the stonework up there.

2) We’re talking BIG sandstone blocks rather than bricks, so doing a normal stepped flashing doesn’t appear to be possible.

Any ideas? Should I just go with the original plan of patching it up?

If it’s an old property and has been water tight up until recently I’d carry out a repair similar to the original design.

However, if you are cutting a diagonal cut into the stone you can wedge the lead flashing in place using lead wedges (and seal with lead sealant)

If you have scaffolding up then I would get a trusted roofer to sort it for once and for all. It will probably be cheaper than you think and will give you peace of mind for the next 10 years.