Mercedes 1995 E300D install second oil pressure gauge
 

I have a 1995 E300D Mercedes and would like to install a second oil pressure gauge. I seen this post here back in 2006

http://www.peachparts.com/shopforum/diesel-discussion/278961-mechanical-vs-electric-oil-pressure-gauge-comparison.html

Here the person install a fitting in the oil filter cap in place of the center bolt. Not sure if this is a good idea, any other ideas where I could easily install a fitting and a second mechanical fuel pressure gauge.

Thanks for the help.