Like the posting here over the years if you get too heavy handed with locking the filter handle[group head] in, or the seal needs replacing so users over tighten the filter handle, that rotational force will bend and eventually break one or more of the lugs that hold the brew head collar in place. It is only die cast metal - not repairable and not available as a spare part. [My broken collar looked exactly like the one in this other post]. The symptoms are significant leakage from the brew head.

So for the heavy handed amongst us, just tighten enough so it does't leak and don't overfill the basket with coffee.

I was fortunate to be able to find a repair agent who scavenged one off another Em5900/Em6200 but looking at the listing in the service manual it was never available at any time as a spare part. Perhaps I need to think about a replacement long term, e.g. BES920 or EM7000, maybe if a good special appears? For the time being the old faithful continues to run - as I prefer my coffee without milk the underpowered steam function does not worry me too much, and I have found the right grind / temp/ beans / single wall basket to keep me happy.

PS I hate throwing things out that might be repairable, too much wastage and landfill these days