Hi Jack For the price of the seal it's a no brainer, if it leaks when you refit it you will have to strip it all again.
Just finished replacing the thermostat on my 250. Said i'd post a how-to once done so here's some info. Tools: 8/10/12mm spanners/ratchet set (need an 8mm spanner to get the bolts off the thermostat itself, awkward to access) Method: Remove battery (I drew a diagram of where all the wires went just incase) Unclip the ecu (I presume this was the ecu.. the box with 3 plugs at the front of the battery casing) *remember where all plugs went Remove battery casing and surrounding attachments You will then see the thermostat (3 bolts attaching 2 pieces of metal bang on in the middle of the engine, do not get confused with the air flow pipe leading to the manifold towards the front of the engine) Proceed to remove bolts (very fiddly but persevere ) Once removed you will lose a bit of coolant but not much Make sure you insert the new thermostat the way the old one came out Resemble everything (this is where the diagrams come in handy) I then left the car running with the cap off the coolant bottle for 20mins to get rid of any air in the system Let the car cool and then check how much coolant needs to go in Jobs a good en! Took roughly 2.5 hours.
