As above!

Also worth noting that they don't like being filled with oil too quickly, especially if you're using a funnel and hose as the air can't get out quick enough and you end up with a big air pocket rising and pushing the oil out when you get close to passing the 1.5L mark. So don't try and cram all 1.9 litres in in one dollop. I've found adding 500ml in stages, leaving short time between each to let things settle.

You are not alone making a mess - at the 600mile service the dealer managed to get oil everywhere which blew all over my legs when I rode the bike home! (Only time it's been to the dealer)

As for the horn, it is most likely to be the spade connectors need a good clean and roughing up to bare metal again. Spades are notorious for corroding, particularly when they are exposed to spray like on the Tenere. You can check the horn itself by taking it off and connecting it directly across a battery.

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