Timing Gear Replacement

[BeetOls]

Isuzu engines are known to utilize timing gears, particularly their pickup and crosswind lineups. Is there any life span for these before it finally needs replacing? I know they might be able to even last longer than your engine's life (before needing rebuild) pero hindi ba nagkaka allowance den or play ang mga ito...therefore causing more noise? Mileage is approaching 215,000kms

So my quandary is...should it be on my preventive maintenance list? This came to mind because i once saw a hilander with it's timing gear set being replaced due to reasons that the customer was complaining of the engine noise.

TIA!