Thank you all for the additional comments.
Will check the pressure relief valve first.
Then do the Vaseline prep before spinning up without plugs / sparks.
Between my father and i we've had the car for nearly 36 years doing just 10,000 miles over that time and quite often its not been used or run for a few months and never seen this issue before. Its always had fresh oil typically 20/50 and filters every 2/3 years over that time so should I hope be in great condition internally?
I will be interested to see the condition of the relief valve and pump gears to see if any damage that could have caused this.
Keep you posted.
