Here is my thread on the lift pump O-rings:
http://www.peachparts.com/shopforum/diesel-discussion/383438-om603-602-601-lift-pump-re-seal-o-rings.html
If it's been since 2014 that the fuel filter was last changed, it's probably due. Good time (and excuse) to change the O-rings on the filter bolt while you're at it.
The rubber lines back at the tank are worth a look. If they're oily or cracked, time for replacements. If they're dry and look ok, probably can ignore them for now and focus on the more common under-hood stuff. They're not subject to the heat and stress of the engine bay and tend to last longer. I pulled the originals off my SDL back in 2016 when I R&R'ed the fuel tank and they were still fine but I replaced them anyway.