Issues with dpf and using alot of oil

[Maya]

Need some advice and wondering if anyone knows anything that can bring some light. 
2 years ago my car was running fine, I never seen any oil lights until I took my car in for an mot and service(I was advised to change my fuel injector seals and then I was told the car wouldn’t start and i had to repair all 4 fuel injectors, that was dodgy as it was but since then I’ve had issues with the oil.. 

When I got the car back from the mot/ service, and fuel injector work, the engine light appeared as soon as I drove off from the mot and service
Since then , a mechanic I trust , shown me two new changed Injectors, rather than 4.
We’ve been trying to establish the oil leak for so long. 
In June 2022 my dpf blocked up; I had it cleaned, it filled back up quickly 
Again the mechanic I trust said, usually you clean the dpf.. and have no issues come back.. unless there is a problem with the engine?

Overall the engine is smooth 
I’m spending a lot figuring it out
I’ve used 1litre oil a week sometimes 
I’ve also noticed a huge amount of oil on the undertray 
The car has been in limp mode for a while due to the dpf which I will either delete or clean again, but why so much oil loss ?

A new garage has said these things 

Rocket cover leaking 
Front main oil seal leaking
Sump Leaking 

I have previously changed the seals and rocket cover so I don’t think it’s worth to re try this (as a garage that previously looked at my car stated)

I can visually see a huge amount of oil of the undertray 

My main concerns are the large amount of oil useage (sometimes 3litres a month) 
And the dpf, I don’t think cleaning it again will resolve it, some people are suggesting deleting it will resolve a lot of issues ?
How true is this?