S124 SLS hose fitting
 

I’m replacing the rear suspension hydraulic cylinders and hoses on my 87 300TDT.

I can’t figure out how to connect the new cylinder and flex hose to the hardline fitting. The fitting on the hardline doesn’t move. I expected it to rotate like a brake line fitting. I’ve circled the fitting in the pic.

Is the fitting supposed to rotate or am I missing a trick to the hose on?

It looks like there is a tack between the flare and the tubing nut which would prevent the nut from turning.

It's supposed to spin, but likely rusted, fused to the tube inside the fitting. You can try Kroil or PB blaster and shoot it in the backside of the fitting between it and the tube, and soak it good giving it time to work it's way in. Gently see if it will free up.

Inspect well before starting to work it in the event that there is a back weld as Sugar Bear indicated. These types of flares are usually meant to spin just like on a brake caliper.

that fitting is, for sure, supposed to spin. hit it with a propane torch.

X2 heat it until it's cherry red then spin it

If it won't turn, could you turn the hose onto it instead?

Pre twist the plastic line
 

When I replaced a leaking strut years ago, that nut would not turn. I
'pre-twisted the stiff plastic line and turned the strut as much as possible to then insert the line in and "unturn" the strut so the fittings could be tightened. Awkward but doable.

Nice work to replace the rear suspension.