As they say, when it looks to good to be true, it usually is. Looking at this ad, I think it is certainly a case of too good to be true.
- only 1 photo of the vehicle on the advert, seems strange....
- almost no information regarding service history, general conditions etc., seems strange.....
- $3500 for a 120k kms V6? Would be an absolute PIG for that price! Even trashed V6s with 180k kms + go for around $4k - $5k, so for $3500 the owner is either an idiot, or has a total POS (I bet on the latter, hence the lack of photos and info)
- You would be lucky to even get a decent TS for that price and mileage! A good TS at that mileage isn't much less than $5.5k - $6k generally
Then lets delve a little deeper. The new gearbox and the subsequent low price is probably due to the diff blowing and destroying the gearbox. Generally, so long as its repaired/replaced competently, this wouldn't really be an issue. But since the car is only $3500 for a V6.....something leads me to think this car has some major mechanical issues. Perhaps not with the diff/gearbox but there has to be something wrong with it. The seller is basically giving the car away at that price, so there has to be a catch somewhere.
Sorry to be a pessimist OP, but having spent almost 12 months looking at various V6s and TS' before I bought my car, this car is WAAAAAAY too cheap to be a good one. Spend at LEAST double that and you might get a decent car. But most genuinely good sub 150k kms V6s are $10k+ and knowing the 916s, don't buy one on the cheap unless you're willing to spend the several thousands of dollars to get it up to scratch.
Just my 2 cents