|What size is your C partition ?|
How much free space is left on it ?
I searched using: MFT in use: 99%
and looked at several pages of "hits"and found nothing that confirms there's a problem with that.
I used Defrag to Analyze all the hard drive partitions on a computer I have - 8 partitions, 5 are MFT in use: 99%, the other three are 97%, 95%, 45%.
None of the partitions are anywhere near full. Windows is probably as fast as it can be with what I have loaded.
References referred to on the pages I looked at....
How NTFS reserves space for its Master File Table (MFT)
Files Excluded by the Disk Defragmenter Tool
Percent MFT in use = 99%
JSI Tip 0487 - What is the MFT (Master File Table) and how can I manage it?