If you have to replace valve seals, would you have to remove any or all of the fuel injection sysytem?

My car started using oil so Buick place here started an oil consumption on it due to a bulletin they had about the possibility of bad valve seals. Hey did replace them. However, my car has not run right ever since. It has had trouble with lots of hesitation like it's not getting enough fuel or something. They have had it twice and they are saying that it never does anything when they drive it. I know better. It doesn't do it all the time. It's sporadic but when it does, it makes me wonder if I am going to get left stranded. Here is my question, would they have had to remove any part of the fuel injection system when they did the valve seal replacement and if so, could they have damaged or not done something right when they put everything back together?
I'm sorry that I don't have any money right now to make a donation and sure won't have any if they have to do any kind of repairs on my car again.