Ok so I removed the left axle to replace the boot and I suspect I lost all the gear oil.

I went to the auto parts store and had no clue on what type of fluid or how much to buy...

Any advice?

Also can you top off fluid with engine in place?

You can use a good quality 20/50 oil (I used Castrol GTX) in the gearbox. The filler plug is on the side of the gearbox (Right side, looking from the rear) just behind the drive-shaft. It is a square plug--and it will be TIGHT. I used a short, old 1/2 in drive extension bar, tapped the 'female' end onto the plug and then a socket (or spanner) on the 'male' end. You fill the gearbox until it just comes out of the fill plug. Don't forget to put the drain-plug back in--fairly tight.

Thanks Hobbler. I will do this tonight. And if the fuel tank is clear after inspection I may drive it for the first time in five years. I accidentally left 3/4 of a tank of fuel in there while I was away (5years) ...

I'd dump that fuel to give yourself a fighting chance. Fuel goes stale remarkably quickly and will definitely give starting problems.

The low temp volatile fraction is the first to evaporate off.
In a modern fuel injected car this is normally not a problem as the injectors will have a fine enough spray for the mixture to ignite but in a carburetor this spells trouble, hence why on lawn mowers and classic cars and bikes you need to drain the petrol before the winter lay up.

The gumming up comes from the ethanol, it allows bacteria to grow, wipes out pipework, glass fibre and plastic tanks plus has its own deposits too. E10 is now being introduced so expect issues to increase.

Yikes. Can I clean the tank myself or should I/must I take it to a specialist?

The tank has a drain plug - but you need to be super careful when removing draining etc...
1 Battery disconnected
2 well ventilated work space
3 good wide funnel into a fuel canister - only ever use item made for gasoline.
4 drop it off at local disposal depot
5 leave tank with cap off and drain out to vent out outside for 24 hours
6 drain plug back in - install tank - refill and off you go.

About the gear oil. If you have a 126 gearbox you must use only a GL-3 or GL-4 gear oil. Do not use GL-5 rated oil or this will damage the syncros.
Proper gear oil is an 80w90.
John

A short while ago, for reasons I won't bore you with, I needed to change the oil in my (126) gearbox. I spoke to the experts at "Castrol Classic Oils" The advice from them was that their XL20/50 engine oil was the correct oil for the gearbox. Engine oils and gearbox oils are graded differently, and it turns out that there is very little difference between a 80/90 gearbox oil and a 20/50 engine oil. Some while ago there was quite a long discussion on this subject on this forum, but I can't exactly remember when