Decided to change the Mercedes header tank on the Stag for two reasons, firstly it has developed a leak along one of its seams, and also because I've always been a bit concerned about access to the spark plugs on that side of the engine. Both problems were not insurmountable, a better location nearer the fusebox would have worked and I could probably have applied some appropriate gunge to the tank to seal it.
In the end I decided to go the route that many Stag owners have followed and fit the Stagweber aluminium tank that has been designed for the Stag.
This in itself has shown up a slight installation problem, my alternator is located on the upper nearside of the engine which leaves very little clearance between the bottom of the tank and the alternator fan blades - about 5mm. This is I think a result of using a belt of the same length as the power steering, looking closely at it would suggest a slightly shorter belt will alleviate the problem.
The Tank is now fitted and seems to work well, all I need to do now is fit a low level warning light as the tank has a level switch. I will probably utilise the seat belt warning light which no longer works as I have non standard seat belts fitted.