I'd give it a good going over with saddle soap, that'll certainly remove any mould residue, and also treat the leather.
I have a leather steering that's been out in the shed for some time now. After a good clean it all looks super. However after a day or so it has a light covering of white residue. this I believe is some kind of mould residue.
What kind of products can I use on it.
Please don't tell me fairy liquid. It dosnt work.
I'd give it a good going over with saddle soap, that'll certainly remove any mould residue, and also treat the leather.
Leather is a tough one to clean.
Generally most car interior leather cleaners will contain waxes and silicone. Ideally you want to avoid these.
The best way I find to keep leather clean is simply wiping with a damp cloth.
And feeding it with a good leather wipe.
Saddle soap will break down the finish if untreated.
SADDLE SOAP
Clicky linky
Leather is very easy to clean, but again, use water VERY sparingly. Leather is porous, even in a coated (excluding patent leather) finish, and will absorb water like a sponge, ask any biker.
If you use a damp cloth, wring it out fully, and then allow the leather to dry naturally, do not use artificial heat, as this would dry out the leather, and lead to cracking.
Oh, and btw, never use fairy liquid on leather; amongst all the other chemicals, it includes sodium chloride (salt), which would definitely be very bad.
SADDLE SOAP
is what you use on horse riding equipment
Might sound a bit mild, but Autoglym do a nice leather conditioning kit which includes a leather cleaner and conditioner, with this you have no chance of damaging it with something too strong.