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I don't have that unit, but my RCBS is very similar and it has a round part with O-rings with a female thread in it that pushes down on the lube stick like a thin piston. Sounds like your analogous part is missing.
I would start by contacting Lyman for a spare parts drawing, so you can verify what is missing? If the same part in the 450 and 4500 aren't identical, it wouldn't be hard to make on a lathe. Perhaps your local vocational school likes to have its students take on that sort of project? But, since lube sticks haven't changed size ever, I expect the same part fits the newer and older units.
I don't have that unit, but my RCBS is very similar and it has a round part with O-rings with a female thread in it that pushes down on the lube stick like a thin piston. Sounds like your analogous part is missing.
I would start by contacting Lyman for a spare parts drawing, so you can verify what is missing? If the same part in the 450 and 4500 aren't identical, it wouldn't be hard to make on a lathe. Perhaps your local vocational school likes to have its students take on that sort of project? But, since lube sticks haven't changed size ever, I expect the same part fits the newer and older units.