Nikkor 18-135mm and Sigma 70-300: Repair or Replace?

[loretedelpy]

I am the owner of three lenses, two of which are currently broken. My question is whether it is better to repair these lenses or if the money is better spent replacing them.

Broken 1:
[h=1]Nikon 18-135mm f/3.5-5.6G ED-IF AF-S[/h]Diaphragm problems- Repair estimate $130

Broken 2:
[h=1]Sigma 70-300mm f/4-5.6 DG APO Macro[/h]They say circuit problems- Send out for $20 + the unknown cost of actually fixing it
I'm not so sure what the problem is- the issue is that it no longer detects aperture from the camera. This happened once before several years ago at a wedding and I remember there being a switch I had accidentally bumped (which I found, switched and it worked fine). The manual, (which I can't find at the moment) says there is a manual aperture ring near the mount which needs to be in the A position or I will have this exact problem, but neither I nor three other people I had look at it could find said ring. There are many reports on the internet of people with this problem finding the aperture lock and having the problem fixed. So when I brought it to the repair shop, it wasn't because I thought the lens was broken- I was just swallowing my pride and asking them how to use my own equipment I've had for many years Should I just assume the aperture ring lock and not "circuit problems" are my issue and bring the lens home, or should I trust them and send it out. And if I do bring it home, any hints on where the aperture ring lock is?

(Still working: Nikon 50mm f/1.8D AF)

 

[loretedelpy]

Here is a link to the manual (thank you Gary Huston)
Sigma 70-300mm User Manual - a set on Flickr

The aperture issue is listed on page 2:
<For Nikon AF/MF, Minolta MF>
When you use the program exposure mode or the Shutter speed priority auto mode, the Diaphragm control ring must be set to the smallest F-stop (i.e. largest number). All Nikon AF/MF lenses have a safety button which should be moved to the lock position (fig2).

And on page one, fig2 is shown an aperture ring and its lock button.

I have the Nikon version of this lens. "All Nikon AF/MF lenses have a safety button which should be moved to the lock position (fig2)." I cannot find either the aperture ring or safety button. How is it possible I can't find this component of my lens?

Super thanks to anyone who can solve this mystery.