1999 E300 Bolt for Tensioner and diesel leak
 

Any idea where i can get the bolt for the idle tensioner that looks like a small shock absorber? I guess there is a top and bottom bolt that goes into the eyelet.

https://www.pelicanparts.com/catalog/SuperCat/3743/MBZ_3743_ELCHRG_pg4.htm#item17 bolt for this part drive belt tensioner shock

Also, I have a diesel leak at front of engine when I stop the car. I would say it is a Substantial leak, especially when my diesel tank is full. Any thoughts ideas or experience?

If I understand your question, this link might help, it should show the related part #'s

https://www.mboemparts.com/v-1999-mercedes-benz-e300--base--3-0l-l6-diesel/maintenance-and-lubrication--belts-and-pulleys

On your fuel leak, I had a similar problem when I bought my car and found it is one of the most common problems with it and similar diesels.

The plastic fuel lines and associated o-rings get old and brittle resulting in leaks. There are lots of posts on the subject if you do a few searches.

https://www.pelicanparts.com/catalog/SuperCat/3743/MBZ_3743_FULFUL_pg1.htm

look for 'fuel lines with fittings' and you should also source ' viton ' rubber o-rings for longer life

Replace all the fuel lines, and the shut off valve o-ring too. Mine always leaked a bit the whole time I had it even after doing all that, the delivery valves were leaking pretty bad when I sold it too. That's crazy how expensive that lower bolt is though.

Shut off valve o rings

I had forgotten about the little o-ring on the shut off valve on top of the fuel filter. Mine had that problem also.

Another problem I had with the fuel filter mounting was one of the black plastic connectors on top of the fuel filter housing had a very tiny crack that was seeping fuel.

Being in Texas and not needed the fuel heater, I bypassed the heater and the small filter on the engine side of the fuel filter housing. From the fuel tank metal hose below the washer fluid, i ran a new hose with a fairly large in-line 50 micron filter and from there up to the fuel pump inlet. I snipped off the old plastic line and slipped my new fuel hose over the remaining stub and tightened it with a small worm gear clamp. It's been about 4 years and probably 40,000 miles and no problems. Doing this eliminated a couple of the clear plastic lines and also had a larger inside diameter hose to the fuel pump.

I believe the fuel hose was Gates Barricade 5/16 lower pressure version ( cheaper ).

https://images.firstcallonline.com/parts/img/documents/gat/gatesbarricade4page.pdf

I'm thinking about installing a washer fluid tank in the trunk and using the freed up space to install a low pressure fuel pump plus a 2 micron fuel filter with water drain. My hesitation has been in not knowing which fuel pump would be reliable enough for continuous operation. This would quickly allow locating any leaks air/fuel in the clear plastic lines plus eliminate any possible vacuum created by the existing fuel pump.

The dealer wants $70 for this 'bolt'... its really a bearing.

I have gotten by with a new arm if the 'bearing' / bolt is not that bad.

the fuel leak... narrow it down to either the fuel lines and orings on the entire system... or the injector pump seals. Then buy a complete set of orings or seals for either system. very likely to be the orings on the fuel system with all the complex hoses and whatnot.

I forgot to mention that I found this bolt for about $20 recently, not from the dealer... I just made do with what I had.