Wife drives a 1995 Mitsubishi. The car is driven gently and has only done about 40,000 miles in all these 8 years. All this time, it's been using dino oil 20W-50 (various brands). Bear in mind it's hot & tropical here, it's 86-90°F everyday! So I'm thinking of doing this at the next oil change: 1) Flush the engine 2) Replace with Castrol GTX 15W-40 Good idea or not? I'm primarily concerned about the flush. Don't want any leaks or increased oil consumption after.