Diesel Tuning Dude
Join Date: Jul 2007
Car: 75 Tourer Conn SE & 45 TDi VNT
It depends how you define frequent - it's a known issue of these cars but many of these are well in excess of 100,000miles, some have never gone at all.
So whilst it's common enough to become a known 'feature' of these pumps, it isn't that common itself.
Faults with the timing mechanism can in theory cause the same issues that a failed timing solenoid would - however I've personally not heard of this.
Personally i'd be tempted to try the solenoid, but obviously it's hard to guarentee these things. Might be worth checking it's resistance though and see if it's gone open circuit or failed in an externally verifiable way etc before splashing the cash.