HI Garrett, yes, this problem does effect some e510 users attaching FL50. I had the same problem. After some time the screws holding the hotshoe become less tight and the hotshoe starts to wiggle under the strain.
The solution is easy - you need to tighten the 4 screws holding the hotshoe in place. They are on top of the hotshoe, hidden under the small black metal plate. To reveal the screws, you need to slide the plate back.
The procedure is explained here:
You don't need to understand the Polish commentary, just scroll down and look at the photos.
Hope this helps.
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