Hey John,
From your description ~ jerky at full lock, it sounds like you may have a pressure problem.
If it was just a seal, it would be a simple case of replacing it & the bearings as well.
With vane pumps, when they loose pressure its often that the body is scored & the vanes damaged. Not wanting to be a prophet of doom but that is what you describe. In such cases a rebuild is a waste, even on a cast iron bodied Vickers.
When you pull your spare down, have a close look at the vanes & body.
Good Luck !!

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving