I was looking on the OPIE Oils website and came upon this product sold by Millers:
Engine Oil | Running In Oil | LIQUID GLAZE BUST
"Millers Oils Liquid Glaze has been specifically designed to restart arrested bedding of rebuilt engines when the normal process has failed.
This product provides wear protection to the valve train and engine bearings while at the same time enabling the piston rings and cylinder bores to commence their correct running in mode"
It has been suggested that one of the possible causes of high M54 oil consumption may be a poor seal between the piston rings and the pistons as the engine has not been bedded in properly.
Maybe this product might help?
I found a bit more info on a post on the VX220 Owners Club website:
Millers state that running in new rings on semi or full synthetic is extremely likely to result in glazed bores - I of course went straight to top Quality Synthetic after 500 miles and after my 6 hour cruise down the motorway... Explains a lot.
I've now got a copy of the Millers technical sheet and reproduce the useage instructions below for information. In effect the glaze buster strips the glaze off and then you restart the running in process as if the rings had just been fitted - I will report back when I've tried it, but it seems logical, isn't an abrasive and made by a reputable firm specialising in oil so here's hoping... It's also not expensive (about £15 for 5 ltr)...
Instructions for the use of Millers Liquid Glaze Bust
It is virtually impossible to run in an engine on modern semi or full synthetic engine oils. Millers Oils produces specific running in oils to overcome this situation.
In the event that an engine has been rebuilt and the running in process has not been satisfactorily achieved, it is possible to rectify the situation with the use of Millers Liquid Glaze Bust.
1. Drain the engine oil, but do not change the filter.
2. Refill sump with Liquid Glaze Bust to minimum level on dipstick. Ensure vehicle is on level ground, as this is critical.
3. Start engine and idle for 2/3 minutes.
4. Stop engine and refill to minimum level on dipstick.
5. Drive for 50 to 75 miles with engine under maximum load. Ideal situation is pulling hard in second or third gear up a hill at the peak of the torque curve.
6. Check oil level and refill to minimum level. You should not be worried to see considerable oil consumption.
7. Run as above for a further 25 miles.
8. Check oil level and refill.
9. Repeat the process up to a maximum of 200 miles OR until oil consumption reduces.
10. Drain and refill with Millers Classic Running In Oil 30.
11. Run as para 5 for a further 500 miles.
12. Drain and refill with Millers engine oil to the specification of your vehicle.
13. Replace oil filter.
14. Check oil level and fill to maximum mark.