Most good bathtub replace will recommend replacing a gate valve regardless of its condition. The time to discover if it will work is not during a flood in your bathroom. If you have it replaced with a ball valve then check your water heater and laundry valves, too. Have them replaced at the same time with premium ball valves. Ball valve laundry bibbs make it easy to shut off the water to the washer after each use which may help to prevent floods in the future.
Examine the washer and replace it with a new one. Also replace screws in water line repair case they are old and damaged too. The new ones you buy should be durable and of good quality.
If you bought the same unit it should line right up, if you were unable, you will need to remove or add length to the existing piping. This may require you to splice together copper with plastic, don't let this scare you the hardware store will have all of the necessary parts.
Working on the gas lines is also a complex job that only a licensed plumber can handle because it is very dangerous. Small leaks can't always be detected by odor alone, but a licensed professional has the proper equipment that's needed to ensure that you don't have any leaks in the line.
When the drain line stops up it is just a matter of calling an air conditioning contractor to come out and clear the drain line. While he is there he will add an algae preventative to the system to prevent future occurrences. Proper air conditioner maintenance is the key to preventing water line repair leaks.
People who own rental properties are great ones to give you information. With all of the service people needed for maintenance on their units, they typically know who to call and what level of work they perform. Most property owners will be more than happy to give you the information you seek. In fact, they were probably in your shoes at one time.
Then, you can take your new shower parts home and reinstall them in the inner assembly. It is very important that everything be aligned properly and tightened to prevent leaks. Beware of over tightening, however, since this can also cause problems. Once you are sure everything is installed properly, replace the cover plate and turn the water back on to test your repair work. With a little bit of work, your do-it-yourself shower repair project can be a success. It does not take an expert, just a little effort and know how.