It does sound like the laser on your PS2 is dying, not your game. Pick up a second hand one from an electronics shop; that's what I did.
Though give your disc a good clean as well. If they are scratched, some of the damage may be repaired. I think Blockbuster do this thing where they send off scratched CDs, games and DVDs and get them re-coated. That may help.
Buy yeah, it is likely to be the machine. (bleddy PS2s...
The PS1 was far more robust...)