Contact the manufacturer. These things are not listed for unit repair using random hardware store parts. Expect Hydro to disapprove any funny looking repairs.
That is not simply a lever. There's a mechanism in there, that is important to the ability to "break" high current flows.
Do not attempt any repair without consulting with the manufacturer. If this is a common thing with an easy and proper fix, they will have it.
Regardless, this job is a big problem because this equipment is hot at all times. If it's before the meter, even pulling the meter will not de-energize it; which makes working on it a dicey affair even for an electrician. This is an unfused load that could pull as much as 25,000 amps straight off the transformer. At this scale, arc-flash gets serious.
It is excessively rare for me to say "this should not be DIYed", but if pulling the meter won't de-energize it, I so say. In that case, to de-energize it, they would need to get in a bucket and go unhook it from the pole line. Once thus de-energized, have a field day, but again don't do any repairs the manufacturer doesn't endorse. I would sooner just replace the box with one that will be reliable.