Well I thought I would check my chain stretch as this is an easy painless one, got a 10 degree stretch so putting in a new chain and tensioner tomorrow. Rails are all still in good shape very light shade of tan. The PO must have used the old chain when he changed the rails.
See if that helps the old girl out, I hope it at least relieves some of the burden and lets me lean it up a bit not going to hold my breath though, I still think it is electronic and am going to use Steve's O2 sensor test after the chain is in.
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)