As Mark said, not a Poulan. I'd bet that saw is 6-8 years old, and many parts are no longer available, anyway from anywhere it seems. The oiler is a weak point, and different than the MacWannabes. Seen/know of three now with little use and are parts saws because of that.
A041=small Poulans, Efcos, Huskys. Have an oiler hole.
K041=mid size Poulans. No oiler hole. Same slot width, very similar tail profile to a K095, or small mount Husky, which when modded to oil from the adjustment hole, work very well for this application.
T041=something I've never seen
True A041 mounts do not use a oiler hole. Same mount that is used on the S25's, wildthings, small Echos, Huskys etc, with a little smaller tail profile then the K041 mount.
A T041 is a A041 with the Intenz tighting system in the bar.
XPLRN, your getting confused even farther as the bars you show are not Oregon bars.
The one on your 4000 is a Windsor made bar and they never made a exact Orgon D176 style bar mount. That bar mount from Windsor is actually a Oregon Pioneer/D007 style mount which is very close to a Homelite/D096 mount. If you look at that bar on your 4000 you will find it has a 3/8s slot instead of the 5/16" slot to fit the 5/16" studs on your saw. That bar is supposed to use a S clip spacer when mounted on a saw with 5/16" studs.
Trust me, you want to use a K041 size tail on that saw, a D176 tail is alot larger and brings the chain too close to the top of the cover on that saw.
The proper bar for that is easy to find on ebay or any Oregon dealer. A quick look on ebay showed me all these.
NEW Poulan 20" chainsaw bar 3/8 Pro 3450 3500 3600 3750 & MANY OTHERS chain saw | eBay
NEW POULAN ECHO 20" BAR & CHAIN COMBO 3/8 050 70 DRIVER | eBay
POULAN CRAFTSMAN ECHO SEARS 20" BAR 3/8 050 70 LINK | eBay
NOS POULAN PRO BAR 530 044556 1650 9211 VC 3/8 | eBay
eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices
NEW POULAN ECHO 20" BAR & CHAIN COMBO 3/8 050 70 DRIVER | eBay
POULAN - 20" Chainsaw Bar Fit 3350,3450,3650 FREE CHAIN | eBay
I'm sure your starting to get the picture by now.
One thing to notice is that all the above listed K041 mount bars are lamintate bars. There are no replaceable tip bars made in that mount in 3/8's pitch.
If you want to run a better replaceable tip bar you will want to run a small husky mount bar in the Oregon K095 style. You wil have to modify the small Husky bar to oil through the adjuster holes like your original does, but thats a easy modification with a round flie or a die grinder. Just file the adjuster hole straight up till it breaks into the bottom of the bar groove.
Be aware though that the Husky mount bar uses a different chain drive link count. For example the K041 mount in 20" uses a 70DL chain, (like your 4000) while the small Husky K095 mount in 20" would use a 72DL chain.
At the sake of confusing you even more, on the Oregon bars, there are variations of DL counts on the same mount.
For example, the K095 mount using 72dl of chain in 20". Oregon used a Z designation on there bar mounts that use a non standard DL count. They made a Z095 mount that used a 70DL chain count. I have one of those modified to oil through the adjuster holes on my Poulan Pro 330 right now.
I know of a member close to me that had quite a few of those bars and he still may have some to get rid of. There the Power Match style bars.