Greetings,
Noticed an intermittent loss of front brake pressure. Bled the brakes which seemed clear of air. During the process I noticed that operating the lever made a wet air sound at the m/c piston. No obvious leaks of fluid in the area but I sprayed contact cleaner over the join of M/c to twist grip housing which bubbled under pressure. Assume I have a leaking cup or seal. Fortunately I have a used spare which appears in good shape. 
I’m off camping in a few days so wanted to crack on but didn’t have any crush washers for the brake line banjo at the M/c. At a pinch I will anneal the old washers but managed to get some for delivery tomorrow.
Three questions:
1) Does the team think my diagnosis is correct re leaky cups/seals, or should I look elsewhere in case my swap doesn’t work?
2) Could I have used a Dowty washer instead of the copper crush?
3) I also appear to have some minor blow back on the ‘newish’ bleed nipples. Is it ok to seal the nipple to caliper join with a little silicon grease?

Thanks folks. Very keen to get back into no UK lockdown life and get the bike out on a 2000 mile welcome back ride.

tinyspuds wrote:Greetings,
Noticed an intermittent loss of front brake pressure. Bled the brakes which seemed clear of air. During the process I noticed that operating the lever made a wet air sound at the m/c piston. No obvious leaks of fluid in the area but I sprayed contact cleaner over the join of M/c to twist grip housing which bubbled under pressure. Assume I have a leaking cup or seal. Fortunately I have a used spare which appears in good shape. 
I’m off camping in a few days so wanted to crack on but didn’t have any crush washers for the brake line banjo at the M/c. At a pinch I will anneal the old washers but managed to get some for delivery tomorrow.
Three questions:
1) Does the team think my diagnosis is correct re leaky cups/seals, or should I look elsewhere in case my swap doesn’t work?
2) Could I have used a Dowty washer instead of the copper crush?
3) I also appear to have some minor blow back on the ‘newish’ bleed nipples. Is it ok to seal the nipple to caliper join with a little silicon grease?

Thanks folks. Very keen to get back into no UK lockdown life and get the bike out on a 2000 mile welcome back ride.

(1) YES (2) YES (3) IV USED Girling brake grease without any problems just around the top of the thread.Fitted new nipples at later date

Cheers Mo. Stu.

Edit note: slightly concerned about the cheesy grin on the new nipples comment.