Ah scottish borders, the flag on your profile said norfolk island which I thought is a tiny island well off the coast of Aus and Nz, I was imaging what a fight it would be finding anything for a 3c there and how much post would cost
![Smile :)](./images/smilies/icon_e_smile.gif)
There's a few places doing 3c stuff in the UK, I like using tractor spares because the stuff always turns up quick, but there's vicary, john charnley and quite a few others. The JCB's of the 3C series until the powertrain 3c3 were based off a tractor skid, so the skid, gearbox, engine etc are based off leyland tractor offerings which helps spares availability.
The sight glass tube is in the front right side of the cab vertical below where the front bucket/loader controls are (well a bit in front). Its just a long clear tube that fits to a spigot on the top and bottom of the tank.
The next problem when you find it is that its often difficult to see the level unless someone has replaced it as hot oil seems to make them really opaque with time. I have on occasion got by with a really strong floodlight and squinting a lot, but when I got that mk2, someone had fitted the snapped off tip of a fishing float inside the tube to give something to focus on when the hydraulic oil discolour's everything, which I thought was a really great but simple idea and is on my todo list. That tube is also pressurized mildly when the machine is running I believe.
There is a position you have to have the front loader/bucket/rear dipper/arm/bucket in to check the hydraulic oil level correctly. I printed that page out of the manual downloaded from here and laminated it and leave it in the cab to remind me because I always forget exactly which bit needs to be where.
If you look at the hoses that are hanging looped that go up into the boom/dipper, its possible on some that they just haven't refitted the hose guide clamps after replacing them though one looks far too long to start with. There are a series of alloy & plastic clamps inside those sections that keep the hoses constrained, and then you can clock the hydraulic connections while tightening finally so they have loops in at the moving junctions to cover movement but don't rub. On my machine, none of the hoses in the rear section were clamped when it arrived, just bits of string or nothing so they just slid about in use.
The cab doesn't look too bad and it has all its glass still & saveable with some tlc also. Looks like a good basis for a project!