Hi
I had the same problem with my 2002 JGC 2.7 this year.
I had a mobile Merc specialist down to North Wales from North Yorkshire.
He dropped the gearbox and engine,removed all the injectors and serviced them.
Removed all the carbon deposits.
Re cut the injector seats in the cylinder head.
Replaced all the stretch bolts and sealing washers.
Carried out a diagnostic test on completion.
He carried out the job from the back of his van and under a tarpaulin(it was raining) next to my house which took him eight hours.
His cost would have been £550 but he replaced one of the injectors with a recon injector(£60)
Total cost was £620 all in, with a 20,000 mile or twelve months warranty.
The engine looks like new and runs sweet as a nut. I can highly recommend him.
He can be contacted on 01423 862204 or 07577 473486 or email: indigomerc@aol.co.uk
I would use the mobile number as he travels all over the country doing this job.