The hood latch on this 300D doesn't lock very well in the 90 degree position.
Today, I changed fuel filter and primer pump, and I was trying to the air out of the system get it to start. It almost did several times and shook quite a lot.

Well, this jostled the hood loose, and it slammed down before I could stop it. Now, I can't get the hood open.

It appears a bit lower on the driver side. I pull on the inside hood release and I feel a resistance, but I'm afraid of pulling too hard, lest something breaks.

The doesn't drive yet, so driving down a bumpy road is not an option.

Any tricks?

Try to get some lube up in the mechanism and the hood release cable. Not sure about the one side being lower, could be a missing or collapsed rubber stopper, and the hood is cocked and jammed because of that, you could put a 2x4 with a large towel wrapped around the end up from under the car maybe and push up to see if you can get it to release. I had this happen on a Karmann Ghia once, yeah it was a real bugger to get unjammed.

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1983 W123 300TD US spec Turbo engine, with Euro bumpers and manual climate control, and manual transmission.

The hood on my 300td (not sure if mechanisms are the same) won't open unless I have someone putting slight pressure on it while I pull the release. I've learned that the weight of my toolbox is enough to press it down when I'm by myself. I feel like that may be a trick I learned on this forum...

When I first got my 85sd,while working on the AC I had the hood way up and when I quit for the day it came half way then stopped.
I pushed a little and then the corner went through the windshield the hinge had broke.

After that after that my trusty 2x2 was never far from me when working under the hood
Lesson learned
greazer2be

The lube part, and with a second person a little force downward on hood while pulling hood release. Where any tools left in there when the hood closed, may be what caused the extra tension, ask me how I know.

Yeah, tools was my first thought. I *think* I got everything outta there...

I'm gonna try pushing down while helper pulls cable. I tried pulling up while helper pulled, but not down. I have squirted oil all in there and made a mess.