On a hill you'd simply use the handbrake when launching the car to avoid rolling back...and many modern cars with manual transmissions offer hill-start control/hill-start assist features...
Oh the headaches those hill assist solenoids cause on Subaru's. Especially when they start to wear out or get electrical issues.
Never heard of this, is it common? (Old gf is a subi mechanic but she has never mentioned this but i usually hear about what common problems exist in subi's)