As I see it, you have two options.
1. Replace the blade with an OEM blade. Don't trust a used one.
2. Replace the fan with an electic one.
You might want to check out if there is a new blade available. On my 91 XJS, the orginal yellow blade was prone to cracking, there was a factory replacement made of black platic, I recall hearing, but i can't remember where, that the same black blade was used on the XJ40 as well as the XJS.