You can lose fluid into the transmission, unawares except the reservoir level drops. I have a 2017 that has had a flawless slave piston, so it has gone unchanged. Don't know anything about new hoses since I haven't needed to. The a big positive change for me was the 2019 thin Belleville Spring and pressure plate with higher preload. Two parts, easier pull. One way to avoid brake-air-entrainment issues when a bike is laid over or goes upside down is to always fill all brake reservoirs to overflowing when you put the cap back on. Let it run right over the edges and onto some paper towel. Zero air is needed between the fluid level and cap bladder.