GLS Class (X167) Produced 2020 to present

M256 Bolt corrosion

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Old Feb 14, 2026 | 05:43 PM
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GLS450 E400 E350
M256 Bolt corrosion

I notice significant corrosion on the bolts holding down the fuel rail (?) on my 2022 GLS 350 engine. I know this are gets incredibly hot and we park the car outside in the PNW so I assume its a worst case scenario for corrosion. Does anyone have any ideas for a fix or prevention? I assume most protectants would burn off in this location.

M256 Bolt corrosion
M256 Bolt corrosion
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Old Feb 15, 2026 | 11:06 AM
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From: Colorado
'21 AMG53 wDPP & ARC, 19 GLC300 - Former-03 C240,2 ML BlueTecs,20 GLE450 E-ABC,15 Cayenne D,17 Macan
I'm assuming that you have a GLS450, not 350, since you say it's am M256.
Are those nuts made of brass? Often nuts in high heat applications are brass, and it's less of an issue.

I'll have to take a peak at mine. Are those visible with the engine cover on?
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Old Feb 15, 2026 | 05:24 PM
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GLS450 E400 E350
Yes GLS 450 is the correct vehicle. The nuts appear to be brass and judging by the corrosion the bolts are steel of some kind. They are easily visible with the engine cover off.
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