Chain off / pushrod snap / casing damage

[unfazed]

thanks again for getting back to me; I genuinely do appreciate it.

I have had a look on ebay and have seen the pumps you mentioned. I am just wondering if this sounds like a reasonable / best plan of attack:

1) remove and replace pump (with new oil seal) [do I need to drain sump first? service manual suggests not but surely there's a risk of oil leak, or is that only when the system is under pressure?]

2) flush/check/refill coolant system to make sure my bodge has worked

3) replace pushrod & seal [am I right in saying that to do this correctly I remove front sprocket and then retaining clip for pushrod seal, as opposed to forcing one into the gap?]

4) providing the above has all worked and leak free, replace sprockets, washer, nut and chain

sorry for all the stupid questions, I really am a novice at all things mechanical but am keen to use this opportunity to learn as much as I can, but of course don't want to risk damaging the bike any further.

Thanks again.

No stupid questions there  Download the manual in the downloads, it shows the pump replacement on it.

Buy or borrow a  torque wrench as bolts are all arounf 10Nm and easy to over tighten if you are a novice at this.

You are better off draining the oil, replacing it and the oil filter, on the off chance there might be coolant contamination of the oil. Unlikely but always better to err on the safe side.

Use a sealant on the pushrod seal to ensure sealing against the crankcase.
Oil/grease the pushrod and the seal edges before inserting the pushrod.
Oil/grease the pump seal and crankcase where the seal will be also before installing.
There is also a seal on the outlet pipe which will need replacing.
Yes remove the sprocket and the seal stopper, makes the job easier.

The piece of the crankcase that was broken where the sprocket cover bolt and dowel go could be built up with plastic metal (JB weld or something like it) and the hole for the sprocket cover bolt and dowel could re drilled and screw hole tapped

Get the new 12mm nut (9mm still on yours) and tab washer. This has to be tightened to 90Nm