Its your choice to take it to 3S, I have never been to any 3S dealer for my LIANA. Going to 3S dealers make the maintenance expensive, not LIANA 
Neither the parts are expensive, they are head to head in the cost with Honda and Toyota parts, only slightly lesser. In markets like Plaza every single part of LIANA is available and that also in quite lesser cost than any 3S dealer will quote you.
You can use any of ZIC, Caltex, Liqui Moly, Mobil, Fuchs.
Use DK of Korea, or ABRO of US, if you are really looking for saving costs.
Using any Coolant, without the recommended mixture concentration will serve no use no matter which brand you use. LIANA will consume 4L of coolent, so buy packs accordingly. And yes please don't forget to flush the existing cooling system with clean water a couple of times prior to fillig in new coolant.
3S sells filters at some idiotic prices. From the market you can easily get good imported filter in less than the half price, look for brands like VIC, NITTO. Find some reliable auto shop who can give you quality products in better rate.
I am currently using a Korean made filter, sorry forgot the exact brand. All good branded filters will serve you good for 8K kms as like the 3S ones.
And yes please stay away from the Guard filters.
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