The IPs mostly do not fail - they leak and need to be resealed. With the advent of recently mandated ULSD (15 ppm vs 500-1500 ppm sulphur) the seals shrink and the lubricity reduction that has resulted does impact the fuel elements which receive their lubrication entirely from the fuel. The question of whether the IP has been used with SVO/WVO is really not relevant - unheated veg oil can result in coking and deposits on the piston rings and valves, but WVO/SVO does not otherwise "damage" the pump itself and it's increased lubricity may actually do a better job at lubricating the pump than old fashioned #2 when it had at least 500 ppm of sulphur in it.

Used injection pumps can be had for between $100 and $350 from eBay and Mercedes wrecking yards with all or most of the components still attached (VCV, ELR, ALDA, stop actuator, etc.). A properly rebuilt pump will replace any worn or damaged hard parts and all seals, recalibrate and test delivery. Average price for this service at most Bosch depots is about $900-$1000, some diesel shops can do it for a bit less, $750-800.

The biggest complaints with these near bullet-proof IPs is the aforementioned oil and fuel leaks - they tend to leak oil from the bottom cover, sometimes the rear cover. The lift pump can get noisy and occasionally leak at the gasket. The delivery valves tend to leak when the o-rings shrink. Problems with ALDA and the stop actuator are common (ruptured diaphragms). ALDA can be rebuilt, but the stop actuators are sealed units (but not expensive). ELR is electromagnetic and has only an O ring behind it which can occasionally spot a bit of oil.

To achieve the original 0-60 times, the IP should be resealed and re-calibrated (at the minimum) and 150-200K miles is probably a good rule of thumb even though they will continue to work pretty well while leaking with weakened springs. They certainly won't last as long on a diet of the new ULSD #2 or the increasingly rare #1 fuel which was already quite low lubricity compared to the old #2. Biodiesel blends of B2-B5 do a good job of replacing the function of the sulphur and do a better job with no significant loss in coloric energy per litre (no appreciable loss of mileage).

Buying a spare IP may be prudent if you can buy a good used one for around $250.00. You can have the "spare" resealed/recalibrated at your leisure while you tool around with the "old" IP until you are ready to have the resealed IP installed and timed per the FSM. While you are at it, you should consider having the injectors cleaned off, nozzles cleaned or replaced (Monark's are my current favorite), pattern, flow and pop tested per the FSM within a range of 135-145 bar, with no greater than 5 bars between any two injectors (balanced). I also take a hard plastic bristle brush to the pre-chambers and check the glow plugs, replace if old after brushing out the bores.

I wouldn't be a afraid of a used injection pump and the spectre of the WVO/SVO hobgoblin should not frighten you either.

Warm regards,

-bh