We definitely need more goals but are you really serious about us being "sound defensively"? We seem to need a 3 goal lead to be comfortable (and that hasn't happened for a long time).
Tonight was a great example - we dominate the game but 1 screw up and suddenly we spent the last 20 minutes in "about to lose it" mode.
Goals conceded:
Chelsea - 24
Everton - 27
Spurs - 29
Arsenal - 29
Liverpool - 30
United - 31
Only Chelsea and City have conceded less goals than us. However, goals scored:
United - 59
Chelsea - 49
Arsenal - 48
Liverpool - 42
Spurs - 41
Everton - 37
Our defending is fine, really. We have this strange difficulty with keeping a clean sheet, but we rarely concede more than 1 goal (which is why i find your statement about us needing a three goal lead to be comfortable a bit strange).
Far and away our biggest problem is that we don't score enough goals. While Arsenal, Chelsea, and Spurs can put 3 or 4 past a team and put the result beyond all doubt, we can't.
We've scored 3 goals or more on three occasions this season, Spurs have done it six times, Arsenal seven times.