You can undo the bolts. I have removed cyl head after all bolts have been torqued down to spec. Reuse the HG after it has been installed. No damage done. Make sure all the holes are clear of any oil to prevent hydro lock when bolts are torqued down. I normally spray the bolts with WD40 before I put them on. I don't think you need to oil the cylinder head, oiling the bolts is the same.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.