Welp, looks like the Merc is going nowhere soon. Can't remove the injectors and broke one of the plastic fiitings on the fuel return system. Fun times!
The plastic tubes are very brittle after a while and there's not a lot you can do but replace them, but the injectors will come out, you just need brute force and the bolts will undo, then just make sure you retrieve the copper washers ( gaskets).
Aye, that's the plan. Was surprised how brittle the plastic was, took no effort to break. I'll have another crack today, there's a bit of play on the injectors so hopefully they'll budge with patience or ignorance!