blue landline phone, vintage style, not working perfectly (Sciennes EH9)

Having a clear out and found this nice looking phone, I think it has at least one loose connection because I'm sure it wasn't working reliably so I stopped using it. Checked it over prior to posting this so I could say what the problem was, but it was working fine. I think it was the sound that would come and go. If you've got technical know-how and think you could fix it, just thought I'd check before I bin it.