[chrisf]

it's very tight fit, any liquid present is going to make it seal that much tighter. I test fitted an insert before I had removed all the old oil, and it was very very difficult to remove it. A lot of suction going on there. Tight enough to crack something if enough water were to freeze and not be able to expand? I don't know, maybe.

Now that I think about it, heat is transferred from the insert to the strut, hot to cold. Any liquid between the two will aid or impede this transfer. I guess antifreeze would be about the best to transfer this heat?