Coolant Loss....VRS PD 170

Hi guys

Its a long time since I checked in but seems there is still a huge wealth of info on here.

I've been out of the country for the past couple of years with work, and in between that time my brother has been looking after my car.

Before I left I noticed a small amount of coolant loss every couple of thousand miles, but this has moved on a good bit over that time and I'm now topping up the coolant up every 200-300 miles which is pretty concerning!

I'd read about the PD engine having a porous head and suffering from minor coolant loss so never really thought much of it, with the current amount of coolant loss I figured there must be a leak in the system but cannot see anything obvious at all and the system was pressure tested which didn't show anything up, plus I've not noticed any deposits on the inside of the oil filler cap or oil mixed in with the coolant.

Got to admit I've been scratching my head, but after another search on here, a few of the posts I've read point to the EGR valve which I'm guessing will also account for a grumbly sounding turbo.

Anyone had anything similar and ideas of my next steps? Replace EGR valve costs versus Darkside EGR Delete Kit?

Even after dropping that money will I still have a grumbly turbo? Expecting this to hit the wallet hard!