Menards has Formula Shell for $.79 a quart after rebate, and only $.99 a quart before rebate. Is this stuff worth saving $.15-30 cents a quart over Chevron Supreme, Havoline, or Exxon Superflo? I like the idea of a $5.45 oil change for my Tercel! Or how about if I used half cheap Shell and the rest GTX or Havoline or something? Thanks!