It's amazing how we still get enquiries from people who come across the old article in Practical Boat Owner (PBO) discussing the resealing kits we used to supply.
These used the old Marine Seal 033 two part butyl putty which you mixed and then applied almost like a linseed oil putty for the sash windows on an old house (like mine). There was a primer too which became questionable to ship. The putty took two weeks to cure, so you had plenty of time to rework.
Though 033 was used in the industry for many years, we've been using specialist silicone sealant since 2017 and have stopped supplying the kits. Silicone is better, but it's yet more critical to ensure surfaces are completely clean and you get one shot at a good fillet.
So for these reasons (and other) we don't consider Silicone a DIY option and thus don't supply kits using Silicone. We also don't stock the old putty and to be honest I'm not sure we can even source this now.
Bottom line is if you want your windows to be leak free and have a professional look, then we'll be happy to refurbish them for you.