Took the plunge and bought an old Clark forklift. Need help with identification and a few questions. Looks like a "Carloader" from comparison to photos saw posted on web. Has side access doors to engine that have two mesh grilles in each and open upward with hinge at top.

Has 4 cylinder flathead? gas engine looks like original paint on engine is medium blue. Seems to run well.

Seller said it was 3500 lb capacity, but don't think they knew anything about forklifts beyond what who they bought it from told them.
I worked as a ASE certified auto tech for a few years back in the 70's and have pretty good mechanical knowledge overhauling engines, transmissions, machinery, electric motors etc., but this is my first forklift.

Questions:
SERIAL NUMBER LOCATION FOR ID
I read somewhere serial number was on frame, someone posted was :"under battery" which looks to be in original carrier on right side inside the access door. Took out battery and took a quick look, did not find anything under the accumulated crud in that area. Before I scrape too much, am I looking in the correct place?

BRAKES
When I got it home, the brake pedal did nothing - went to floorboard with no resistance or braking action. Looked in master cylinder and it was about ½ full of fluid. That was yesterday. Today I went out in garage and pumped the brake pedal a bunch of times, and now it has resistance, firm not spongy near the top of it's travel. Did not have room or time to start it up and move it, but I could hear something moving inside the right front wheel when I pressed on the brake pedal and I put the machine in neutral and rocked it fore and aft a little with a 2x4 and pressing the brake pedal stopped me being able to rock it, so maybe the brakes do work? I'm not one for fixing it if it ain't broke so will add some brake fluid and try things out when I get some time. Any ideas on why no pedal yesterday, OK today?

HYDRAULIC OIL MILKY COLOR
The oil in the hydraulic tank which is in front of the motor, sort of under the front of the seat looks milky. Very pale green tint maybe. Does not seem foamy. Any idea why it is this color? How high in the tank is the level supposed to be, and what oil to use? Can I get the 5 gallon pail of tractor hydraulic fluid/trans fluid and use that? How about automotive automatic transmission fluid? The lift seems to work OK and it has no major leaks, the lift cylinder area especially is dry. The little bit it does leak somewhere leaves a few drips on the floor at right front of the machine, maybe a few inches overnight. The radiator coolant looks clear light green like someone did use an antifreeze mix in it, so there does not appear to be comingling of coolant, though I don't even think these systems are interconnected anywhere.

ENGINE OIL DIPSTICK
Where is the engine oil dipstick and any idea how much oil goes in the motor and oil filter part numbers?

Thanks for any help.