djinn:
Welcome aboard! As far as 300D or 123 goes, the easiest thing to do is just put the year and model of your car in your signature (click on the "user cp" button on the top right of this frame). Then you can say 300D in your posts and anyone who would be able to help you would already know it was a 123.

As far as your post goes, you answered it yourself. The vacuum hoses are the hoses right above the oil filter housing and if you knocked any of them loose (which is common during oil filter changes), the resulting loss of vacuum will cause your problem. Find which one is leaking and your problem will be solved.

The ignition switch cuts the fuel to the IP via a vacuum "switch". No vacuum = no shut down. Additionally, cars with leaky vacuum systems will sometimes need to run for a few minutes before they have stored enough vacuum to shut down via the key switch. The vehicle stores vacuum in a few locations which is why you kept hearing it when the car was off.

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1982 Mercedes-Benz 300CD
1982 Mercedes-Benz 240D - stick