1984 500 SEL and gasoline odor problem & few other questions

Just bought this excellent condition 84 500 SEL for $2000! and am excited, but it has a couple of issues I was wondering if people here might know about (nothing good found after google searches):
there is a very strong gasoline odor in the car both while driving, but also it is particularly strong after car sits overnight closed up. What should I check? Is there some sort of special filter that is going wrong?
Dashboard (speedometer etc.) not lighting up - is there a way I can get a fuse diagram online somewhere to help with this?
Also, the text below the heater/climate controls is in German, but the speedometer is in MPH - I'm wondering if this was a European vehicle imported to the US? or were American controls written in German? (luckily i speak german so no big deal - just found it interesting)
How much mileage can I expect to get on the original engine on a well maintained 84 500 SEL? Anything special I should do at this point? it has 280k miles on it. A few years ago in Calif I had a 76 300D that was at 400k miles and kept chugging I presume (sold it, and miss it!)
Thanks for any info...
JR
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I believe the fuel tank is in front of the trunk - behind the back seat. The tank is probably leaking, possibly at the top where the fuel gauge is inserted.
You could also crawl under the rear axle and looking up inspect for evidence of fuel leaks form the fuel lines etc.
German marks on the controls and cloth seats indicate a gray market non-US spec car. These were imported in the late 80s (due to their relative cheapness in Germany vs. US market prices) and converted to conform to US law, thus the MPH speedometer.
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It is common for old hoses to start leaking... Usually the leak is where the fuel pump is... right by your passenger rear wheel... if you see braided hoses... that's original. The major problem with replacement of these hoses is that the fuel tank would completely drain as you remove the hoses... so better to work on nearly empty tank and have a empty gas tank to store them.
I would check for old hoses in the engine compartment too.
Dashboard light is controlled by that knob on the left side of the cluster... turn it to the right and you should see the light come on brighter... if not, you may have broken rheostat... easily replaced and cheap... or bulb. You just need a thin wire coat hanger with a hook on one end... insert right next to the cluster about 2" from bottom... on the side... push in and turn 90 degree and then pull the cluster out... take your time not to damage your vinyl dash.
It is possible you got a grey market car... looking at the VIN number usually tells you if it is a grey market car... if it says something like W126... instead of WDB...
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