the cooper d diesel engine is same as peugeot citroen ford 1.6hdi, so what you cant find parts wise with a mini brand you can always find cheaper buying under the above brands ie timing belt kits turbo's etc, infact i have a 58-reg cooper d clubman that had a snapped glowplug and had eaten its engine oil due to injectors seals and build up of crud on the turbo oil feed pipe,, cut a long story short, i ended up buying a bare cylinder head out of a 2005 ford focus replacing the valves and guides and reground seats with new seals, cost for head £50, other parts a further £100 as the glowplugs on these engines are very long and when snapped off major pain so secondhand head is cheapest way forward.. so head changed pistons out honed bores new set of piston rings, replaced big end bearings and fit new oil pump and strainer, must add i have rebuilt 1000s or engines in the past,, car has done 108k cost up to this point of rebuilding it £350 also bought a garrett turbo £275 and dpf well better not get in to that.. important note always get engine as hot as you can before trying to undo the glowplugs on these engines,, done cold they will prob snap off.
all this could of been prevented by doing this,
at around 80k, change injector seals. remove sump and clean it right out,(ie build up of gunge) also i always run stuff called seafoam in the oil to clean out carbon build up. remove the filter gauze in the end of turbo oil feed pipe, and if was me replace the turbo complete, also the dpf filter will need changing as will be full and cause back pressure and heat carbon build up that kills the engine,, when turbo fails on these engines due to impeller shaft oil seals failing they go in to a overrun due to the engine oil being burnt like diesel,, so engines revs at 10k untill oil has all gone,, after they never feel right after this has happened...changing oil and use a flush treatment at half the makers recommendations is also better than doing nothing.
. SEA FOAM TWIN Diesel Petrol Engine Injector Cleaner & Fuel PK 2 Motor Treatment | eBay
the above link is seafoam but one can in oil 100 miles before oil change and the over to a tank of diesel cleans all systems very well i have found.. infact use it before rebuilding stuff and insides of engines are spotless if used for the 500 mile they suggest