Lead in contact with aluminum

[Futsal]

I have a shutter that uses a lead weight to counter the weight within the frame of the shutter. The shutter can be opened and closed by hand and the lead counter weight connected by cable and rollers slides up and down an aluminum extruded section that forms part of the frame. The problem is the lead ingots are jamming over time making the window hard to open. Ambient temperatures are 7 - 34C and these shutters are on solar faces. The building is near the sea.

My questions are:-
1. Will the lead ingot change shape over time thus causing the jamming? If yes, could this be foreseen? If the lead bulges it will jam due to small clearances to the frame.
2. Should the lead have been enclosed in a metal casing that could slide more freely within the extruded section?

 

[cloa]

How much is the clearance- it might just lead sulfide formation or aluminium corrosion.

 

[Futsal]

Haven't measured but from what I've seen, when new around 3 - 4 mm.

 

[EdStainless]

My hunch is corrosion products are forming and creating friction that causes the weight to bind.
A plastic sleeve over the lead might be a good idea. Make sure that it will handle the temp. It should side better.

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