It's a V7 Special
Nice choice of bike. I'm pretty sure that yours is a European spec V7 Special and not a US spec Ambassador. If you scratch under that black paint you will probably find the original white paint. The frame number can confirm it.
Be assured that these bikes are bullet proof and I can see nothing alarming in what you have experienced so far. Mine displayed many of the same symptoms as yours when I first bought it completely original with 80000 Kms on the clock. Spent the first winter fettling it then rode it to the Isle of Man from Denmark with my eldest son and all of our camping gear on the back! I'm still running the original chrome bores after examining them from up under the crankcase with the sump pan dropped. I will eventually fit the Gilardonis but with regular oil changes (including sump pan off for cleaning) and close inspection the engine could probably run to 160000 Kms before needing a full rebuild. Acknowledging, of course, that if the chrome bores do start to deteriorate unchecked the chrome particles will potentially destroy your engine. See Bloodweisers excellent thread-
Notwithstanding, these bikes are beautifully engineered and easy to keep on the road. Most of the parts are still available in Europe. So, what I'm suggesting is to keep fettling the way you have been to eliminate all the little things before digging too deep. Here is what I did:
Brake shoes, wheel bearings, careful brake adjustment.
Cleaned the crankcase breather and fitted new rubber hoses.
Fitted new washers to the banjo bolt connections for the solid oil lines feeding the cylinder heads.
Removed all of the clutch and gear change linkages, All were worn oval so I tapped in new bushes and fitted new pins. Reinforced the clutch cable bracket under the battery tray to prevent flexing.
Replaced all original cables.
Replaced a few broken spokes and fitted Avon Road Riders - don't be tempted to go wider than stock. They handle much better on standard sizes and the modern compounds are so good now.
Fitted new fork seals and sealed the chrome seal covers with JB Weld. Used 30W fork oil.
Changed all oils a few times within my first 1000 Kms of ownership to flush it all clean.
Set valve clearances, ignition timing, and rebuilt carbs (mine were running lean at higher revs). Fitted a Dyna Ignition Booster into the original ignition system to take the load off the points - very reliable and durable upgrade and only one wire to reconnect to revert back to original.
Re-wired the loom as necessary. Especially around the fuse box and wired a relay into the starter circuit to take the load off the original starter switch. Also wired in mini relays for the lighting circuits.
Re-plumbed the cross-over fuel lines to incorporate a filter.
Reconditioned the generator and the starter motor - only needed a good clean, lubrication and brushes.
New air filter and rubber boot.
For all that, mine probably runs better than when it came out of the factory in 1970. No leaks, intentional but clean gear shifts, smooth clutch, comfortable suspension, and very reliable. The brakes remain the only limitation at speed, Starts first time every time no matter what the weather and I wouldn't think twice about riding it RTW with a sensible tool kit. It really is a legendary old bike.
To remedy your oil leak double check the crankase breather hoses including where the solid hoses enter the bell housing. Check the waste hose and it's location. Also, double check the valve cover gaskets and their seating. My left one leaked at revs on long hauls and managed to run oil down over the lower LHS of the motor and onto my left boot. I had to add a smear of silicon gasket goo to the gaskets to cure it. The other culprit may be the centre banjo bolt for the solid cylinderhead oil feed lines. It is awkwardly located under the generator.
Best of luck with it.