1995 Holden Statesman Hi Our Vs 6cyl Had 3 Crank Angle Sensors Replaced Last

Hi our VS Statesman 6cyl has had 3 crank angle sensors replaced in the last 9-12mnths and we can't work out why?? We have changed the Harmonic Balancer as well and still it has done another crank angle!! Someone said it cld be the timing that is doing it! So just wanted to see what u have to say and if you know how we can do the timing ourselves without a mechanic as this car is sending us broke lol
This car has other small probs also but this seems to be the most reoccurring and the most annoying!! Any advice would be appreciated :)

Cheers Cassie Tapper