Sorry to hear that Martyn.
Fingers crossed for you that it's the cam belt tensioner, as there is a design fault on the 99/00 ones (and even some of thelatter ones) that cause them to loose pressure.
They tend to do it more when weather is cold.
This causes a knocking from the front/middle not too dis-similar to big end failure. Due to the tensioner bouncing on it's end stop when the belt goes round.
The engine in Worzels, before he rebuilt it, was a Subaru return thought to be big end, that ended up being just the cam belt tensioner. But Subaru dealers have a tendancy just to rip the bottom ends out without checking as they can claim it under the warranty and get paid the labour for the job.
|