That sinking feeling

My office chair slowly sinks until I stand up and reset the gas lift.

Occasionally, it will just go straight down, at other times it will stay up all day.

Time to replace the gas lift, so I needed to know the size. Interestingly some sellers on eBay say that they are all the same and offer a single size of unit. Others give you a variety of lengths, though the diameter is the same. The latter makes more sense, so you can already take a guess as to which suppliers to avoid. Then an online search revealed specialist suppliers offering the same parts for half the price. A win, win situation, they don't pay eBay's fees and I get a lower price.