Hi Rik,
It's hard to say, either way, as there are a lot of variables. You'll note I said 'can' rather than 'will' in the post......
The chemical reaction causing the lead corrosion needs a trace of acetic acid vapour in the air to initiate it and then a source of carbon dioxide to keep it going. Basically the acetic acid reacts with the lead to form lead acetate, which then reacts with carbon dioxide to form lead carbonate, releasing the acetic acid to continue the reaction. The issue for modellers is that lead carbonate is less dense than lead so the lead weight swells as it corrodes.
The problem is mostly found with pure lead, such as roof flashing. Lead alloys such as solder, type metal and whitemetal are protected by the presence of tin, antimony, etc. in the alloy. Lead shot, especially the very fine stuff that was sold as 'Liquid Lead' for weighting models is more prone to corrosion due to the higher surface area.
Airgun pellets can have small amounts of antimony added to the lead to harden it, so you may be OK.
The acetic acid can come from many sources such as PVA glue, wooden showcases, cardboard, paper, silcone sealants, etc. etc. and it only needs a few ppm in the air to start the reaction. Was this the model where the solvent in the glue used to secure the pellets attacked the plastic bodywork?
I've no idea about the composition of UHU (they make several types) so can't tell if it might be a source of acetic acid.
It's very hard to make things perfectly airtight and gases can also slowly diffuse through polymers like glues, paints and plastics.
The corrosion starts fairly quickly (months in some cases), so if you haven't seen it yet, you may have dodged the bullet as it were.........
There are articles online by museum conservators on the subject of corrosion of lead artifacts in storage and how to prevent it. I first became aware of it years ago when I spent a few years building glass case ship models, as every book on ship modelling I read warned about casting details in lead but never said why. I eventually found out about the corrosion problem from an article by the US Navy Dept. responsible for the care of their glass case ship models.
I've had no need to add extra weight to anything in garden scale, but in HO scale I add weight using lead flashing cut to fit. Normally I glue it in place with a rubber based contact cement, but in one case I ran out and used cyano- acrylate cement to laminate the lead and fix it to the floor inside a van. A few months later the weight came loose and when I took the body off, the lead had started to corrode and the weight had delaminated. I've been careful to use only contact cement since then and had no problems.
Regards,
Graeme
