Yes, I would get the laser cleaned and the decks serviced, probably best to get a technician to do it.
Unless you feel technically confident to take the drawer unit apart.
Remember to be very carefull when cleaning the lens, as they are very fragile.
Isopropyl Alcohol medical grade is best.
I have serviced many cd decks over the years.
The DN4500 is a great work horse, 1 Denon’s greats.
Lens cleaning could help, but be aware that they are usually plastic. Don’t use excessive force and harsh fluids. Some water and a soft cloth is perhaps the best way.
I would suggest getting the Mechanism drive belts changed, as these stretch and and become brittle over time.
It would be an idea to also regrease the gears, this can sometimes prevent the laser assembly locking up into position fully.
Also check the ribbon connections and control cables to the laser and drawer mech unit, and main board are seated fully.
I have known these come loose, causing intermittent problems.
Failing that, the complete cd drive mech unit can be replaced, which includes the laser and drawer mech.
Cost I would estimate around £50.
There may be an electronic fault, capacitors in the power supply are always favorite.
If you not sure send the unit in for service or contact a Denon service centre for more information.