Stuck brake fluid reservoir lid

Appreciate tips on how to remove the lid of the brake fluid reservoir on my XK120 OTS. It feels like it is welded on. Would like to remove it to check fluid level without damaging the finish.
Also what is the correct replacement fluid for normal driving, ie non-competition.
How often should it be replaced? Brakes feel great but aware fluid should be changed periodically.

Apologies if this has been covered before, quick search showed various opinions on brake fluid, nothing on lid removal.

Thanks for reply Robin. Its the black cylindrical shaped one, on a '54 OTS, Chassis No. S674744.

Can’t help with the lid removal apart from a pair of slip joint pliers with a rag between the jaws and the lid?
For the fluid just DoT 4 or 5.1 for regular or DoT 5 if you want to go the silicon route.

I would just say that I’ll never use silicone fluid again after some frightening failures in normal road use. I use ATE200 Dot 4 in all my classics with hydraulic brakes, and change it every 2-3 years.

A tip for stubborn reservoir caps: get a robust strip of rubber seal - windscreen seal, bit of inner tube, whatever - wrap it tight once around the stubborn cap, and grip the ends with a Mole wrench, very tight. Turn the wrench to undo - think of it like belt or chain oil filter removal tool. This way there’s no risk of the jaws damaging the cap as it’s only the rubber contacting it.

Paradoxically, engineers might use Roger’s method and also start off by paradoxically attempting to turn “tighter” clockwise a degree to break the stuck parts. This principle applies to all nuts and bolts.

Dot 4 only for me as well, due to bad experiences with Dot 5 silcone swelling the seals in my XK120 master cylinder and XJ12 caliper piston seals.

I would try a web wrench aka strap wrench on the reservoir cap.

I never heard of a Mole wrench, had to look it up. They were a British copy of the Petersen Vise-Grip after Petersen’s patent for the Vise-Grip expired in 1941.

DOT4 brake fluid


Thanks very much for the assistance gentlemen! I had to look up Mole Wrench as well, think they’re also referred to as ‘multi-grips’. The web wrench idea looks promising. Will use 2 - the other on the body to counter turn as from memory the reservoir bracket is not solid.

If you wreck the lid there is a great replacement from the early XK150’s that incorporated a float switch for a brake warning light. I have that rigged on my XK140 and it has saved my life. I got mine from XK’s … now Mos…

These adjustable chain vise grips are useful for round objects. Saved the day when I had to remove the covers on some Luvax rotary shock absorbers.


I used silicone for many, many years in the braking system of my Iso Grifo with no ill efects, BUT in the hydraulic clutch circuit it did eventually swell the O-rings on the slave cylinder. Unfortunately, this was an aftermarket co-axial one that fitted around the gearbox input shaft, acting directly on the release bearing - that was an engine out job to put right. I used regular brake fluid in the clutch from then on.

Two episodes, two different cars (a Healey 3000 and a TR), same problem - fluid boiled and let the pedal go to the floor. Both on the public road. It can’t have been anywhere near the advertised boiling point, but it happened… 20 mins to cool down and the brakes were back, but didn’t feel as good as before.