I need to get this sorted out before I order new struts. The strut application charts for all the different manufacturers always list two struts ----- one if your car was originally equipped with "OE Gas" and one if it wasn't. If I understand this correctly, the "OE Gas" units were a little longer and don't have the spacer under them. The "non OE Gas" units were a little shorter and require a spacer on the bottom. Is there any other difference in the two units? I have seen the term "single tube" and "twin tube" mentioned. I think the "twin tube" units are the lower pressure "non OE Gas" ones that are shorter. Without actually disassembling my struts, how do I know whats in there now? Will either new strut fit my strut housing depending on whether I use a spacer or not? This is my first experience with struts that have "replaceable cartridges" and I don't want to order the wrong part.