Putty / mastic / filler / glaziers' compound: right material to repair this skylight...?

[Majdnem]

Hi everyone,
I'm repairing a leaking and partially rotten skylight window. I've started using putty but it seems such a different material to what was used originally that I'm wondering whether I should be using something else... Does putty actually harden to something really solid and brittle like the material I'm replacing (see pics) or is this original material something other than putty? If some other material *was* used, would that have been a mistake? Or am *I* making a mistake using putty (it seems an implausibly huge bead of putty is needed to recreate what was done originally). If so, then what *should* I be using...? Hopefully the attached pics should make that clear: 1) the skylight, 2) the original glazing material, 3) my stalled putty repair.
Thanks!

 

[Stanley services]

Linseed putty is not flexible and therefore cracks as the wood it’s adhered to expands and contracts with the seasons. This then results in areas around the glass where the linseed has a gap where the rain gets in and eventually rots the architectural joiner. The great news is there are two flexible alternatives. The first is from a french company callEd toupret. They provide a mastic based putty which is a lot Easier to apply and is white in colour. The curing time for this is 7 days. The second is from repair care international and is called dry seal. This is easy to apply and cures in a day. There will be residue which you must scrape back the next day and can be sanEd. Cures in 24 hours. Great finish, also in white. Cheeeeeeeers

 

[Stanley services]

Just to follow up. You will need to remove all of the existing putty which is linseed. You will need a putty removal tool and a hammer. Once removed, use 80 grade sandpaper to make the glazing bars straight again. If you don’t then the new putty line will be wobbly instead of straight. Also pre prime the glazing bars prior to new puttty with water based acrylic primer undercoat. If you need to call me for further advice for free, search stanley sash services.

 

[Majdnem]

Stanley Services - thanks! - a genuinely helpful and knowledgeable answer. Exactly what I was hoping for (and my apologies for not acknowledging your reply sooner - hectic couple of days).
So, I've taken your advice: a bead deglazing chisel, a putty knife and the Toupret are in the post (as is just one tube of Repair Care International Dry Seal, but this is more just for me to experiment with - the size of the beading needed means I'd have to buy armloads of these tubes to complete the job). I have 'Dulux Weathershield Exterior Preservative Primer Plus' and 'Dulux Weathershield Exterior Wood And Metal Quick Dry Satin' paint. As I understand it, these are water-based acrylic paints, so fit with what you've advised? (Actually, I was kinda pleased to read that, as I'd bought these Dulux paints first, but then read that putty works best with a shellac-based primer, so bought 'Zinsser B.I.N Primer/Sealer'. Going to leave the one glazing bar I've started as shellac primer + putty + exterior oil-based paint, and do the rest with Toupret + acrylic water-based, as you've advised. And maybe one glazing bar done with the Repair Care International Dry Seal - then I'll have three different approaches to compare. I'll be up on the roof taking notes over the next ten years or so...
Thanks again.

 

[Stanley services]

No worries, hope it goes well. Have a great weekend