I need some assistance here. I have about a foot long portion(straight line) of my ceiling that is making me wonder if a leak from my shower in my master bedroom. THere is a portion of my ceiling that looks like it was a bad tape and plaster job, and it is directly underneath my upstairs shower(where the fixtures are located). I felt this area of my ceiling and directly where the line is and it is a little soft directly on the line. This is not a relatively new line, but it concerns me. The house is almost 20 years old. Does a bad tape job feel soft, or do I have a much bigger problem(possible leak).

Sounds like it is still leaking,open up ceiling to make visible. If not taken care of,will cause you problems. :)

Do not open the ceiling yet. Some shower drains are repairable from the top. Lowe's sells a shower drain that is repairable from the top. If you have a different type then the ceiling may have to be opened. I know of very few that can match a ceiling on a drywall repair. Verify what is leaking first. Use a 5 gallon bucket and get water somewhere other that the shower and check the drain thoroughly. If fiberglass shower, it may be the drain or a crack in the shower. If tile, you may need a new shower pan.
SHOWER LEAKS- there are 4 things you are looking for. 1- drain leak, potable water leak, pan leak, splash leak.
1- drain leak- pour water down the drain only by way of funnel or by hose.
2- potable water leak- leak on shower valve or shower head or piping.
3- pan leak- pan test
4- splash leak- get inside the shower and spray the walls all the way around and check for leaks in wall and caulk and the door sweep. Most leaks are at the door.

SHOWER PAN
PAN TEST- to do a pan test, remove the grid, use a cotton rag, wet it, put it in a baggie and stuff it in the drain to clog it. Then use a bucket to fill the shower with about 2" of water. Use a different source other than the shower for the water. If the pan has failed you will get a leak within 15 minutes.
FAILED PAN TEST- a failed pan test means you are going to removed the shower floor completely to the rough floor and at least 2 tile rows above the shower floor and start over. You will need a drain [possibly] and a new pan at least 6 inches high. No penetrations with nails or screws below the top of the finished curb height. And tile.
SHOWER FLOOR- as for a shower floor on pan material, I would be hesitant. The board may cut or nick the pan material. Most tile guys use a mix to do the pan. Some use the special mix made for a shower floor, some use sandmix which is cement and sand in one bag, and some use mortar mix which is brick mortar and sand in one bag. Using a mix allows it to form to your pan material without sharp edges.
SHOWER FLOOR LEAK- actually, you may think it is leaking at the drain because that is the only hole in the floor. It may be that you left a rock or a nail or anything sharp that penetrated the pan over a period. You may even have a leak at the shower valve and it is running under the pan and leaking out the hole in the floor. However, if you want to open up about 6 inches around the drain and repair, you can. There is an epoxy glue made specially for connecting shower pan material to shower pan material. My concern would be if I cracked the rest of the shower floor.
Eliminate all possibilities before you break up the shower floor.

Have you checked to see if your vinyl or tile is properly sealed at the bottom of your tub? You can get water damage from water getting in where the tub and floor meet. You may only need to remove the old caulk and redo.

I need some assistance here. I have about a foot long portion(straight line) of my ceiling that is making me wonder if a leak from my shower in my master bedroom. THere is a portion of my ceiling that looks like it was a bad tape and plaster job, and it is directly underneath my upstairs shower(where the fixtures are located). I felt this area of my ceiling and directly where the line is and it is a little soft directly on the line. This is not a relatively new line, but it concerns me. The house is almost 20 years old. Does a bad tape job feel soft, or do I have a much bigger problem(possible leak).
There is only one spot of this line that is soft and it is about the size of a quarter. There are no stains on the living room ceiling either. I recaulked the shower at the seams a few months back as it was cracking and chipping away. Ripping the ceiling open seems like a pretty drastic measure. This shower gets used 2 times a day. If this was an ongoing leak, wouldn't it leave a stain or be soft all around?

Do the pan test