I just restored the vacuum lock system on my 240 last summer.

Remember when troubleshooting for your leak, Yellow/Red striped vacuum lines are for lock down function, Yellow/Green striped are UNlock.

I found several leaky area's majority of them were cracked booties on the vacuum elements in 3 of 4 doors. (replaced all)
Also, check rubber seal/grommet in vacuum storage tank in trunk.
There you will find solid Yellow line running into the tank.
good luck
d