So I had a shop recently replace my compressor, condenser, and some other part under the hood near the headlight, but I kept having issues with losing A/C after a week or so. I took it upon myself to pull everything out underneath the passenger side dash and sure enough I can see dye residue with a blacklight around the insulation of the fittings that go into the expansion valve, and it was also wet. I will be ordering new o-rings (I believe it's one per fitting in the expansion valve, so two total), but my question is what exactly does the expansion valve do and does it ever go bad? Since I have everything gutted I don't want to go through this process again. The A/C worked perfectly whenever pressure was good so should I just leave it alone and fix the leak or go ahead and order one anyway? Does the expansion valve work in a way that can contribute to the leak or the system not working properly?

Thanks.