Mani, I'm from the old school of thought, and I would stick with the brand of oil you have used for the 45,000 miles. If you do change brands, which will be no problem, stick with your new brand of oil. There is a school of thought that changing oil brands to often can cause sludge in the engine.
Its a shame that the shop will not correct their error!
500E sway bars
210 16in wheels