WCCC…We’ll service you until you don’t need serviced anymore.
Serious version
WCCC - Large enough to serve you, small enough to care.
Best little Cat House in the world.
or more seriously…
The right part, The first time.
Pleasures for your pus… eh no… that might draw those other type of cougars to you place 
We got the parts to get your Cougar Don(e)
There really should be a mafia line in this, since the boss is a Don
The best parts, the best service - WCCC
WCCC–Cougars come here for service.
or
WCCC–A full service Cougar parts store.
I’m kind of liking this idea. If it works the out the way I think can I have a job? I’ll work for free.
“West Coast Classic Cougar… Enabling Cougar-holics With Prime, Uncut Product Since 19XX” 
(I don’t know what year you started the business; do you count that first $75 parts car as the start of your empire?)
Is your Cougar’s butt sagging?
Do you not spend at much time in your Cougar as you used to?
Is your Cougar not as responsive as she used to be?
Has your Cougar started leaving puddles wherever it sits?
West Coast Cougar has the parts and expertise to help make your favorite cougar look up to 44 years younger.
OR:
One stop shopping for the best parts and expertise at the best prices.
How more perfect than this can you get? Al, you’ve got my vote on this one. No cutesy stuff, just stating the facts, ma’am!
LMAO! Good Stuff!
Slogan: “Get what you paid for.”
Rationale: I think we’ve all bought stuff on eBay or from board members or elsewhere, only to have to buy the same (or the correct) part later from WCCC. WCCC isn’t the price leader on a lot of stuff, but you do get what you paid for - no excuses.
Or if there is an excuse, you know it already from their ACCURATE product descriptions…“crap”, or “fine jewelry”, you know what you’re getting!
What are you saying? Do you mean I’m not getting that on ebay? Ebay sellers don’t omit, mislead, embellish or lie. Do they?
FWIW, I really like Don’s.
West Coast Classic Cougar: Restorations to abominations, we’re here for you. 
+1 for that one… 
This is something I totally dig about WCCC. The fact that the '68 chin spoiler I’m looking to buy says “not a good fit” lets me know that these guys are exactly the kind of company I want to deal with. Not claiming everything they sell is amazing and the best thing ever, but rather giving their honest opinion of stuff-- that is the mark of a great business.
the part that’s over and above, is when it’s a piece of crap, for whatever reason (bad planning, cheap materials, etc…), they say that they will sell it, but only if you insist, and: NO RETURNS! this, in french, is l’heure juste.
Thums up!
How about
“Replacement claws for your cat”
How about… “We Don’t Need No Stinkin’ Slogan” 
Or maybe something vague and generic like “Quality & Integrity”