Plumbers' silicone grease can be purchased at any home improvement store. That's what I use since I ran out of the Eheim lube. Just make sure it's safe for potable (drinking) water use.
I have used a non-petroleum base silicon lubricant on the o-ring on my Magnum 350.-(came with unit/new)- It would certainly be safer. Just a suggestion. 8)
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