On that note...

Depending on the year it will be a DW8 or XUD9 engine.
Both mechanically injected, later DW8 is a slightly smoother lump based on the HDi (DW10) engine which is based on the XUD9 anyway

Either way it would be a simple change to swap for something else, theres the 1.9TD (XUD9TE), 2.1TD (XUD11T) There is also an N/A 2.1 but very rare?

Also been talk recently about a 2.5TD engine based on the XUD in a PSA van which apparently is also a straight swap. (I belive this engine was actually fitted to the Boxer, don't quote me though).

If you do go for a swap then theres nothing to go wrong on these things. Make sure you fit a Bosch pump to whatever you get. More than likely the boxer will come with a bosch pump anyway. All engines should pretty easilly just bolt in, just need to sort out the intercooler pipework and the exhaust. All the coolant pipes are all in the same position and they all use the same universal sensors