I am starting to get a grip on RegEx thanks to all the great help here on SO with my other questions. But I am still suck on this one:

My code is:

   StreamReader reader = new StreamReader(fDialog.FileName.ToString());
   string content = reader.ReadToEnd();
   reader.Close();

I am reading in a text file and I want to search for this text and change it (the X and Y value always follow each other in my text file):

X17.8Y-1.

But this text can also be X16.1Y2.3 (the values will always be different after X and Y)

I want to change it to this

X17.8Y-1.G54
or
X(value)Y(value)G54

My RegEx statement follows but it is not working.

content = Regex.Replace(content, @"(X(?:\d*\.)?\d+)*(Y(?:\d*\.)?\d+)", "$1$2G54");

Can someone please modify it for me so it works and will search for X(wildcard) Y(Wildcard) and replace it with X(value)Y(value)G54?