Weak Spark Plugs and Gear Oil change questions?

Can someone give answers to the following questions?


1) When is the time to change Gear Oil? What if I delay the change?


and


2) What are the disadvantages of Weak Spark Plugs?





Regards,Weak Spark Plugs and Gear Oil change questions?
1)varies as to how hard you are on the vehicle in question, rule of thumb 50,000 miles





2)less horsepower, throttle response, and poor fuel mileage.





i'd suggest not putting them off, if you plan on keeping the vehicleWeak Spark Plugs and Gear Oil change questions?
I've NEVER changed gear oil in any of my manual transmissions.





Spark plugs aren't weak, coils are.
You can get away without changing gear oil for many years and miles in most cases. See your car manual for all maintenance requirements. Don't trust what you hear on the web when you can simply read your manual and get the manufacturer's answer to your questions. The spark plugs in newer cars can last 100,000 miles in many cases.
you need to give more info to correctly answer this question. without knowing what type of vehicle/engine you are talking about nobody can accurately answer, as there are too many different types of engines and or vehicles. not to mention how you use it