I was in the same position as you.....gave birth to DD1 (our first child) in Dec 2007, after a very long labour, ended up in theatre with an epidural and forceps delivery. I suffered a third degree tear (even after the episiotomy) and although I healed well, I DID have some leakage when exercising etc.
I fell pregnant with DD2 in Sept 2009 and had an appointment with my consultant at 20 weeks. He basically explained that, this time, I was AS likely to have a significant tear as any other woman, but not MORE likely. However, he DID offer an elective CS, said that the birth type was my choice and that he and the midwives would support any decision I made. After a lot of thought and discussion with DH, we decided to go for a VB (mainly because I wanted to experience an unassisted VB where I 'felt' the delivery!) However I was concerned that having recovered well after the first tear, another tear would leave me with worse consequences.....
Gave birth in June 2010 to DD2 after a lovely quick 3 1/2 hour labour, with just gas and air (birth was too quick for anything else!). Midwives were very aware of my history and made sure that pushing etc was slow and controlled......unfortunately DD2 presented with her hand up at her face and caused another 3rd degree tear! Cue another trip to theatre, another spinal and 40 minutes of stitching!
However - I recovered well (quicker than before actually) and have no long lasting problems. I count myself lucky that I had TWO third degree tears and have come out the other side fine. That said, we would love to have another baby and I think THIS time that I will go for an elective CS.......I don't want to push my luck!! I think what I am trying to say is that I DID have another tear, but the cause was not my previous tear, but the fact that my lovely mischevious DD2 decided to be born waving at us all! 
Sorry for the long post, hope this helps!