Been riding dirtbikes for 20 yrs, never have had an issue with damaging the fork tubes. Seals yes they do leak, but then so will traditional forks. You change the oil fairly often in dirt bike forks and inspect the seals so maintenance is key. Yes they all use a plastic fork guard. Its all in reducing unsprung weight and rigidity. Last couple of years they are developing and using air forks...no springs inside!