Hello Kester,
Neither of these components would seem to me to be terribly difficult to isolate as a cause - although ‘hole in a valve lifter’ would appear to be unusual, as really would be undetectable camshaft issues.
As you say, as a 16 year old car, the repair bill will likely represent the value of the car, and I guess it’s decision time as whether you have had you money’s worth out of it and are prepared to move on, or if it’s been a faithful servant on which it’s worth further investment.
Since we are talking diesel? here, why don’t you find yourself a local diesel specialist to canvas for opinion?
Kind regards,
Gareth.