The OM602 and OM603 have a different head design than the notorious OM606. The glow plugs are about 1/2 as long as the OM606 plugs and normally won't be stuck.

I've done mine (and helped vstech with his) OM603 powered 300TDs. In both cases a couple plugs were stubborn and had to be worked back and forth gently a little to get them out.

As long as you are not applying gorilla torque you should be ok.

I have heard of people not removing the IM but it requires serious contortion to be able to reach around everything to get to the GPs.

The hardest part of IM removal is getting to some of the 6mm Allen head bolts. Some do not have a clear path of approach for most Allen key tools. Try to use only a flat end tool (not a ball end tool) to break torque. Once torque is broken then you can switch to a ball end.

I would also work with a helper and have them stand by with a claw tool to grab the bolt as it is coming free. It is a major pain to retrieve the bolt if you happen to drop it.

Once you have all the bolts off and the cross pipe disconnected the manifold just lifts off.

I would as a side project be prepared to clean the gunk out of the IM and bypass the EGR if you can get away with it in your location (depends on how strict your vehicle inspections are).

The other pitfall is sometimes the electrical nuts are stripped on the back of the GP and it can be a real pain to get those free. The nuts are *supposed* to be captive on the wire lugs but I have encountered broken retainers before so be prepared if the nut seems loose.

When reinstalling the plugs coat the threads with anti seize. Be gentle on the electrical nuts, they only need to be snug, otherwise you risk breaking the element inside. Also pay attention to the angle of each lug, if they are rotated too far from where they are supposed to be they can short out to the manifold and blow the fuse. Best to check this after reinstalling the manifold to be sure none are shorted.

And yes you will need to renew the manifold and cross pipe gaskets. They are not very expensive and readily available from the forum sponsor.

Speaking of parts, I would only use Beru or Bosch glow plugs.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech