That looks exactly like the engine in our 530-70 that had the corroded timing case issue. Ours was an AK engine but believe the AR to be similar. I actually took our cover off, looked for a new one, almost fainted at the price so filled the cavity in the cover with silicon and it did another two years before giving grief again. We bit the bullet in the end and put a new engine in.
par for the course I am afraid its a well known problem on both the four and six cylinder engines. Someone told me the other day that there are cheaper aftermarket ones available now but when I looked into changing mine a few years ago quotes were £500ish for something cast in what my father would have called "finest buggerum". You have obviously only ever run it on JCB own brand premix coolant and never added water? No? well join the club of people who expected an engine to be made of something capable of holding water.
When I said a few years I meant at least 12/15 years ago and I could only find genuine and the cheapest I found from half a dozen places in the UK and europe were all around £500. I know they are a lot cheaper now that aftermarket stuff is available but early on perkins took the pee. I still have the engine which is basically sound and plan to overhaul and put it into one of our other JCBs when I get time.
with the supply worse than any other company around that time.
