Old thread - but I thought I would add my bit.
I am just replacing the bonnet lock barrel in my 1986 110. It looks like the barrel itself is the same as the door lock barrels (MTC6505), but has a little extension that slots on the end to make the barrel longer (as shown on EaryDeaf's photos). With mine the tab off the barrel is corroded and has broken off inside it, so I am going to have to chisel it out as there don't seem to be replacements available. There don't apple to be any spares for these locks anywhere on the Interweb.
It was a devil of a job getting the 34mm nut off. Heat and threadease plus a lot of choice words with the wrong tools and it eventually came undone without destroying the cast ally outer barrel.
I'll add some photos shortly when I have it ready to reassemble.