It looks like the hose in the first picture could be a suction line and the hose through the filler cap is a return line for the front pump. It will be independent from the internal hyd's.
I am familiar with the spool valves in front of the seat. My 135 has a very similar set up. There may be a problem with the internal controls or linkage but I think the first thing is to understand how the hyd's work. You can't use the 3 pt. and the aux. hyd's at the same time. One or the other and if you have something on the 3 pt., it will creep down over time if you're using the aux. hyd's. The 2 spool valves in front of the seat control the oil flow. The lever on the left directs oil to the side 3 pt. controls (but can also be used to raise and lower the 3 pt. without the precision or constant holding capacity of the side controls). The lever on the right directs oil to the aux. hyd's.
To use the 3 pt., the left lever is pulled back toward the seat and should detent in that position. The odd time it may pop out if lifting something heavy. If it constantly pops into neutral, you can adjust the spring so the detent is stronger. The right lever needs to stay in neutral. Now the side 3 pt. controls will work. To raise anything the outside draft control lever has to be all the way back. The lift height can be adjusted with the position control. Draft control is only used for ground engaging implements. When using the 3 pt, don't pull the position lever further back than transport position. It can be pushed over to clear the stop but that is explained next.
To use the aux. hyd's, the left valve in front of the seat has to be in neutral(middle) position. The draft control has to be all the way up and the position control has to be all the way up as well but even further into constant pumping position. This is when the position control is pushed over to clear the stop(transport position) and pulled further back. Now you can use the right lever in front of the seat to operate the aux. hyd's. There may be adjustment screws on the back of the spool valves in front of the seat and another one on the right side. They also adjust oil flow. I think the one behind the right lever changes it from single to double acting. I'm not positive about the other ones but I am pretty sure all the adjustable knobs should be all the way open or all the way closed. You'll have to experiment. There is a manual on the MF 100 series aux. hyd. operation. I found it on a website called puddingsworld. It's been a while since I looked though. If you are new to this set up, it will seem extremely complicated but actually isn't. I hope I made sense. If not I will try and walk you through it.
