Hiya,
I am facing similar decisions, now 13wks preg with my 3rd. My first labour sounds just like yours - forceps, episiotomy, 3(c) tear. My 2nd labour was great, quick (just under 4 hours), no intervention, just gas & air, but yet another 3rd degree tear (3a).
I had dating scan last week and saw consultant about delivery options... like you, if I hadnt raised my concerns at booking, I think they would just be letting me get on with a normal vaginal delivery, Its only because I've raised my concerns about long term damage to down below that they're now discussing it with me. I dont have any 'symptoms' from the tears now, but apparently its later on in life that things can get 'messy' (if you know what I mean!!).
My consultant is happy to let me have a c-section (we also discussed it at the dating scan for my 2nd child, but it was decided I probably wouldnt tear again....hmmmm... and so I went for natural vaginal), and this time, the consultant pointed out that I am only a third of the way through my life, and the risk is, if I tore again badly, then I might have some degree of double incontinence for the rest of my life. It was at that point my husband declared he definetly wanted me to have c-sect (he was very anti it before, he's now very for it)!!
Anyway, to cut to the point... I am now going to have an endo-anal scan (Lush!) to look at the state of my sphincter muscle... if it looks like all is great and no bad scar tissue, then I may go with another vaginal. If it looks like the muscle is on the brink of giving up / looks in a bad condition, and that any future tear might totally ruin it, then I'm having a c-sect. It might be worth asking if you can have a similar scan? THey dont do the endo-anal scan in my hospital, so I have to travel further afield, but I'd like them to have a look at my bottom (however unpleasant it may be!) before I make a decision.
So, my advice is, perhaps see your gp or midwife and ask if they will arrange an endoanal scan for you, particularly given you are already experiencing symptoms from your previous tear...then you will probably be in a better position to decide which is the best way forward.
Good luck and hope all goes well for you - isnt pregnancy / childbirth so glamorous?!!! I love it all the same though!! x