Interesting, never had that happen. Every once in a while, going under 5mph and trying to put it in first it'll grind but that's literally happened 3 times in two years. Probably was just something I messed up on. I assume you had the clutch all the way to the floor the whole time you were moving the shifter?
If youve never replaced the fluid, its not a bad idea depending on your mileage. One oops grind into 5th shouldnt have generated any shavings of significance though.