I've put this in DIY gear, for some ideas.
I have quite number of rods accumulated over about 60 years. Some are for Mrs Bobfly of course ! Not all handles have top grade smooth cork and have lost infill and some are OK just now but will probably deteriorate a bit.
1. How best to perk up the poorer ones ... what is best for a filler mix that will stick?
2. Is there a stabiliser that can be used to keep the good handles in good condition?
U-40 Cork Sealer seems to be the rod handle sealer product frequently mentioned but hard to locate a UK supplier. Has anyone tried it ?
I can make cork dust easily but what is the best glue. ... exterior PVA, Aliphatic resin?
If it was possible to put the entire length into a vacuum I would go the epoxy route. Personally I would mix the dust with gorilla wood glue and work the mix in to the rest of the handle if there is no vacuum to hand. Hopefully some one with more experience will add to this though.
I don't know, I've never done it.
I'd go with SoldierPmr on the dust and Gorrilla wood glue as the filler. Titebond produce a range of wood glues. These include a mid-brown coloured version for veneer work, mixing this with the standard yellow (or white PVA) might produce a better colour match.
To seal, there are two wood products you could test on an old wine cork. Both are "Sanding Sealers". Leading brands are Rustins and Chestnut. Rustins is shellac dissolved in alcohol. Chestnut is cellulose-based and much quicker drying. You can then finish with a wide range of products (not oil).
To give you an idea this is gorilla with spruce and scotts pine chips mixed.
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I have lots of woodturning finishes including Chestnut cellulose sanding sealer and Liberon spirit sanding sealer with the shellac. I will ask Terry at Chestnut for his thoughts on cork. He sends out a useful weekly newsletter Ken which you can get via their website if you are interested. I have had some emails back and forth recently about a lump of very very resinous Pitch pine.
Glue wise I have Titebond II as well as PVA and aliphatic and epoxy mixes and UV varnish and but it is probably best to avoid a hard and brittle mix.
The U40 cork sealer is used by high end rod builders but for the little I am likely to need it seems a bit OTT to import a pot from the States. Hard to find out what it is, it seems to be a water based varnish.
I've repaired "holes" in cork handles by carefully cutting out a small square box shape with a scalpel or craft knife then glued in a shaped piece of cork with super glue, sanding it back once the glue is dry. Gorilla glue would work but I think the none foaming clear version would be better. Waterproof exterior grade pva glue also works.
Washed seven handles and rinsed off and left to dry. Used Abronet at 80 to make dust, used Titebond II to mix, then filled holes having picked out any poorer looking filler, some was 60 years old, sanded back with 120 then 180 when dried and used cellulose sanding sealer. The sanding lightens the colour but the sealer is light honey so all in all a decent result. Checked over the accumulated armoury of 22 rods ( !!! ) and only 7 spruced up so not quite as much as I anticipated. Will give the split cane job an outing tomorrow. :D