Porous fork slider

This one got me - lack of experience or knowledge, make up your own mind from the following sequence of events:

About a month ago, I noticed what appeared to be brake fluid on the bottom edge of the caliper. Hmmm, not good. Blown seals? A leak somewhere between the MC and caliper. Nope.
Turns out that the substance is not brake fluid but oil. Fork oil to be exact.
Seems to be leaking from the bottom dampener bolt that attaches the slider to the dampener inside the fork. I found a couple of drops right at the end of the fork slider. It had been blowing back into the caliber while riding. This is what made me assume it was a leaking caliper.
Dismantle. Inspect. Replace dampener washer. Ensure no leak from the fork drain hole. Reassemble.
Leak continues. S*&t. B*&gger. Disassemble, check that the fork nut mating with the dampener has no issues. Looks good. Reassemble.
Any one who knows (most on here) how long it take to fill up a fork with 150ml oil know the time you can stand there like an idiot. So this is twice now.
Still leaking.
Lots of swearing from frustration. What the?
Front wheel off. Tape up the whole area with absorbent kitchen towel.
Reinspect in the morning.
No leaks from the expected places, but a few drops from about 6cms up the fork leg. What?
Upon close inspection, the fork leg is porous and was allowing a few drops out every day. This was causing the problem. Not enough to affect fork performance, so not a suspect initially.
Never would have occurred to me.
Disassemble fork. Install new sider. Fill fork with oil again. Reminder to self - buy more fork oil.
The new slider solved the problem.
Al in all, a very time consuming and frustrating process.
Lesson to me: don't take anything for granted. Start with the obvious stuff, but start looking in other places if the obvious areas are not the problem. Am I being obvious?
Take time to understand what is going on.
I wonder if any one has experienced this. Nothing on the search function indicated that there has been a similar problem.
Hope this helps some one in the future.
regards,
JS

I've never heard of that before.

And top marks to you for finding it !

File the surface of the porus section to leave a groove and get the groove welded, dress and polish, as its thick section it should not warp.

Certainly a weird one and well spotted,

Old slider? You've had it years? Or new production? Or new (old) to you bike?

If it's been in service 40+ years, I'd think it's cracking, and preparing to seperate. Had it been porous, it would have been addressed by now.

Not sure of the provenance.

I've owned the Commando for three years, so is some where between 3 and 46 years old.

freefly103 said:

Not sure of the provenance.

I've owned the Commando for three years, so is some where between 3 and 46 years old.

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...and it's had a nuisance leak the whole time you've had it?

No, it just developed over the last month.

I had that happen on a Dunstall fork lower. Of course, they weren't known for quality. This just looked like a little pit, but oil would trickle out. A good clean-up with some brake cleaner and a tiny dab of JB Weld, and it was solved. Doesn't really show unless you know where to look. Couldn't see getting any more involved in a repair than that solution.

Brithit said:

I had that happen on a Dunstall fork lower. Of course, they weren't known for quality. This just looked like a little pit, but oil would trickle out. A good clean-up with some brake cleaner and a tiny dab of JB Weld, and it was solved. Doesn't really show unless you know where to look. Couldn't see getting any more involved in a repair than that solution.

Click to expand...

Good (thrifty) repair.

freefly103 said:

No, it just developed over the last month.

Click to expand...

Do you have any friends that work in the welding industry? A liquid penetrant dye check would be a good reassurance that there is not a bigger crack developing.
https://en.wikipedia.org/wiki/Dye_penetrant_inspection

freefly103 wrote;

I wonder if any one has experienced this.

Click to expand...

Not on a Commando, but a friend of mine with a T160 kept getting a damp patch half way up the fork leg, which always returned after wiping off. The conclusion was porosity.

Reggie said:

Not on a Commando, but a friend of mine with a T160 kept getting a damp patch half way up the fork leg, which always returned after wiping off. The conclusion was porosity.

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My T160's RH slider (a 'double disc' slider, so not an original part) also suffered similar leakage from the outer end of one of the mudguard bridge mounting lugs, so I carefully peened over the porous area using a hammer and a flat nosed punch then sanded and polished it, and it's been no trouble since.

Hi

Yes I have had this before. Early Dommie leg. Someone had wiped it with Araldite.
Older stuff was very good, although Atlas crankcases have been known to be pourous.

As to newer parts!!!
Les was selling Norvil fork legs a little while ago, stating they were pourous!!!!

Chris

Dye penetrant spray comes in an aerosol.
No need to call in favours - Rocol Flawfinder is about £10 retail.
Gives piece of mind/call to action for many things on old bikes.