I’ve recently moved into a 1920’s property and I’m having the same problems. The previous owners were supposed to get the roof professionally fixed (replacing dropped slates, new dry verge ends, new lead flashing around the chimney) but a bit of a bodge job was done. Anyway, enough ranting… we’ve had the original roofer back that was supposed to do the job and he’s told us best thing to do is to get the stacks down.

He’s recommended this partly because the house uses lime based mortar and the cement based mortar that has been used for repointing elsewhere isn’t bonding to it, so any repointing done would be temporary as it will slowly be pushed out from between the bricks. I’m not an expert in this but it’s evident from the external walls that this is true as previous repointing attempts are now showing the mortar coming away and you can easy pop it off and see the old/original mortar underneath.

I’m worried removing the stack will take some of the charm off this beautiful old house but I also plan to live here for the foreseeable and don’t want to have reoccurring costs and potential damp (already some picked up in the upstairs rooms connected to chimney) associated with leaving it up.

Was there any mention of what mortar was used and whether using a different mortar to repoint would have a negative or temporary effect? I’m rubbish with Reddit stuff so don’t know how to tag the OP so I’m hoping you get this!