Downtube braze-ons

Is this a standard part?
No, but you can probably still get one.
Go to a good local shop--they should have an old parts bin from which you can scrap that little plastic piece or a whole shifter. It is unlikely that you can get that old of a part as a replacement through Shimano.

I noticed that the new 7800 series brake/shift levers use this point to attach a cable stop.

Can I keep my braze-ons and use it with new stuff?

Yes. The cable stops fit standard braze-ons

Will Campagnolo gear fit these braze-ons?

Yes

You can still buy new DA down tube shifters. SL-7800

kazam said:

I have Dura-Ace downtube shifters that are mounted on braze-ons. This is old 7400 series Dura-Ace. When I removed the shifters for cleaning the plastic part between the frame and the actual lever broke. They we're just too old and simply fell apart.

Is this a standard part?

If you are talking about the boss covers, I don't know for sure, but I thought that part was common for the previous couple of generations of the Shimano downtube shifters.
See:
bike.shimano.comEV SL 7800 v1 m56577569830536461.pdfOpen ↗

many LBS will have new ones in stock in their small parts inventory for you to compare. They can also be had from some on=line vendors such as:

loosescrews.comindex.cgiOpen ↗

serenaslu said:

If you are talking about the boss covers, I don't know for sure, but I thought that part was common for the previous couple of generations of the Shimano downtube shifters.

Yes, those are the ones! Loosescrews says that they are the same for all downtube shifters and they certainly look like in the PDF.

Great, thanks

/kazam