Originally Posted by perseus
I agree it is difficult to see how this could benefit Japan in any immediate way. However, I expect a presence would have been possible, either due to the German supply ships that made their own surface raiders operational in the Indian ocean, and the 'friendly' Russian icebreaker over the top to Norway!
Perhaps a direct presence in the Atlantic would not have been necessary, an focused assault on British possessions such as India and a threat to the Suez route (as opposed to attacking America) could have made Churchill send some of the British carriers and battleships into a direct confrontation. This would have been the easiest way for Japan to intervene, perhaps with the agreement of Japanese control of an axis leading from the Urals and the Iran/Iraq border East.
Another cooperate venture would be to simply sell technologies German Tanks for Japanese Aircraft Carriers and naval aircraft. Perhaps Hitler could have convinced Stalin to supply Japan with raw materials. A bizarre situation admittedly. However a focus on eliminating Britain before attacking Russia and the US was surely the best choice.
I think the only viable help the Japanese could have given was the continued threat to attack the Russians thus tying down Russian resources in the east, outside that they did attack British possessions in the east but much too late and there is almost no way they could have launched a direct assault on India without securing the other British possessions between Japan and India.
As far as technology goes I am not sure there would have been any benefit in an armour exchange as a 50 ton tiger probably wouldn't have been effective in the jungles of SE Asia (until they reached Australia and India at least) and the Germans really didn't need to be spending resources on a surface fleet that late in the war however they did sell the ME-163 and ME-262 along with other minor technology to Japan late in the war.
On the whole the best chance at an ally the Germans had were the Italians and there failings ended up killing more Germans than the British and Americans combined.