How -  Oil change and they didn't replace the plug properly and oil drained out in 2 days engine sized and damaged.  Checked by Dealership.  

Bare min value = KBB low end of value range

Loss of use  -  This is from Luna v. North star Dodge

We hold that in order to prove loss of use of an automobile, the plaintiff need not rent a replacement automobile or show any amounts actually expended for alternative transportation. We agree with the Washington Supreme Court in Holmes v. Raffo, 60 Wash. 2d 421, 374 P.2d 536 (1962):

If we were to hold that a plaintiff who has lost the use of his pleasure automobile... cannot be compensated because he has not hired a substitute automobile, we would be placing upon recovery a *119 condition of financial ability to hire another automobile to take the place of the injured automobile. The law cannot condone such a condition. He would be denied compensation for his inconvenience resulting from the defendant's wrongful act.

Is there something since then that has changed this court opinion?

Yeah my problem with internet searches so far has been a vast uninterest in doing anything that isn't a major case or they don't do litigation.  I'm not poor but not super rich either.   there are resources out there to help the poor and really rich would either have attorneys for other matters or not care about the $$, but I think I am in no attorney for you land.

Thanks everyone for the feedback...  Guess I will just take it to small claims court and seek the max allowed there of $20,000.   (just as a side question...  If I do take it to small claims court and the judge rules in my favor is there a chance he could determine amount owed exceeds the small claims limit and essentially forces me to take it to regular court?)