So checked the oil level,kicked the tyres made sure everything that should be working did and trundled off out for a ride.
No idea why but on my return I checked the brake header tank [I know I should have checked it earlier] and not being able to see clearly through the sight glass proceeded to undo the filler plug which on removal showed a reasonable oil level but it's frothy.
Any thoughts or observations would be appreciated as long as it doesn't involve spending vast amounts of money.If it does keep shtum and i'll carry on in ignorant bliss unless it's unsafe to do so.

My bus number (if any): RML2478

Frothy brake oil usually indicates a leaky accumulator. There is normally a bit of froth from the oil circulation, but get the accumulators checked. Have you changed the brake oil filter recently?

My bus number (if any): RML2532,GS67,MLL721,MLL738 and an RT.

Firstly can I start by apologizing for my use of a word that has a different meaning to that which I intended.It was bought to my attention and I have duly admonished myself by getting the wife to beat me around the back of the head with a copy of the Haynes Routemaster workshop manual.
Roy I think you were spot on with your diagnosis as I do have a problem with one Accumulator,the filter I also admit I have not changed since Moses's was a boy.This could be something you might like to put on the site as I'm sure I'm not the only culprit who checks Oil ,Water,Lights and such but has never changed that particular filter.

My bus number (if any): RML2478

I've heard it mentioned that a blocked filter can accelerate accumulator problems as the pump has to work harder to pump oil round. This may cause more suction against the accumulator seals so the slight leak gets worse quicker if that makes sense.

My bus number (if any): RML2532,GS67,MLL721,MLL738 and an RT.

A good while ago we had frothy brake oil in 1414, a good while after the last accumulator change/refurb. No pressure drop in the accumulators and filter was fine, cannot remember if we changed it anyway.
After much head scratching and checking all the pipe unions near the Plessey pump in case any air was being sucked in I decided to look at the vent plug which is on top of the tank right underneath the saloon floor, there was a build up of dirt around that area which I cleared off and made sure it was wipe clean by the vent plug which undid fairly easily, however there is not enough room to unscrew it fully to remove as it fouls on the floor above...........
Application of leverage in both directions with a second person on the job carefully allowed enough clearance to unscrew the vent plug the final bit and remove, cleaned up and checked vent was clear and refitted again careful leverage and no problem since.

Mark

My bus number (if any): RM1414 sort of