I live in tropical country and the fuel warmer is leaking. Besides obviously bypassing it, what should I do to the two unused line?

Delete them. Or if you leave the heater thermostat installed, you can leave them connected to it.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Just to make sure stuff. The one one my picture is the diesel fuel warmer correct?

So I just connect the prefilter via hose to the lift pump. Sounds simple but could I just leave the fuel warmer unit there afterwards?

DIY Mercedes Website is selling instruction as on demand video. Which made me wonder if there is anything else to do? mayb capped of the hose or what....

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Yes. The hose from the prefilter will go straight to the inlet on the lift pump (Install new fuel line while you're at it, 7.5mm). You can leave the thermostat in place with the 2 lines still attached, or you can delete the extra lines. It's up to you what you want to do with it. If you leave it attached, considering blowing low pressure compressed air through the lines to get the residual fuel out or it'll drip for a while afterwards.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Just got it bypassed today. So relieved the area is bone dry now.