The L-23 has a 6000 hour airframe life (POH Page 2-9) which may be reduced by dual flight, aerobatics, winch launch or use of wing tip extensions. Given the L-13 experience, there's reason to think it may be hard to get a life extension. You need to set aside $7.50 - $10 per flight hour for deprecation so there's funds available to buy a new glider when the clock runs out on the old one.
To set a price, subtract the logged hours from 6000 to prorate the price less wear and tear. i.e. a glider with 5999 hours would be worth very little. Keep in mind some operators may not have logged all flight time to evade the life limit so if the logs look fishy, walk away.
From my experience, insurance companies are reluctant to pay for repairs to an L-23 so they will total the glider for even minor damage. Premiums reflect this.