original best if it worked right for a long time
gas struts can be purchased from NAPA. You have to choose the following: 1)types of ends 2) open and closed length(s) 3) diameter 4) lifting capacity
Now, these things are usually marketed as replacement units for some original application. But, the mfg catalogs of the unit(s) will give the above info. The tricky part is knowing the weight of what you are lifting(try to use a scale to open said unit). The Diameter allows you to get a relatively shorter piston with relatively greater lifting capacity. Ie: if you need 20 lb lift, you may get it with a 12 inch 3/4 inch piston, or if that is too long, then a 1 inch piston 8 inches long. Now this example is just that-it has no factual info within.
What you have to watch for it the placement of the ends such that the piston collapses correctly and does not try to go "overcenter" when open. Such a condition will negate the ability to close correctly. Also the ends can be expensive, so look for the simplest method of attachment. good luck