Replacing the cap tube may not be hard but, installing the correct size and length can be a pain. Its real important to have the correct one. With your system equalizing so quickly, I would guess that your compressor is bad.
This is why I say don't mess with the cap tube it must be the exact same size and length, and you can not cut a cap tube you must have a fatory replacement available
I've installed many cap tubes that need to be cut in the field for whatever application you may have. The roll came with a chart to tell you what length you needed depending on a lot of different factors (refrigerant,static or fan cooled). I usually scored the tube all the way around with a small file and then it will break apart without leaving any inside blockage. I guess I'm showing my age because that use to be the only way I could purchase and use them.