I have recently ordered a new expansion valve, drier and the two leads on the drier for the aux fan for my 420sel. i intend to replace them and cure my leaky a/c once and for all. My question is that when i replace these items do i need to by some sort of o rings for them or do these parts come with them or even need them. the expansion valve looks like a PITA so I dont want to do it over again and i cant afford to throw away 150 dollars worth of r12. thanks for any replies

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual